LARGE ENGINES AS SHUNTERS
Norfolk and Western were among other roads with large articulated engines intended for a mainline, but used their engines as shunters/switchers as well as evidenced by the following You Tube video  https://www.youtube.com/watch?time_continue=155&v=tEN_wUwzIIE

LARGE ENGINES AS SHUNTERS
Pacific National in Australia has relegated 3000HP ex mainline units to shunting and transfer duties in Melbourne, Adelaide and Perth and most likely Sydney and Brisbane as well. There were two ex Victorian Railways C class ( mechanically the same as an SD40-2) hood units and a couple of 81 class (or a big 66 class)

LEAVING FREIGHT CARS ON THE MAINLINE AT LOADING POINTS  
by  Bill Beech
A book about the Yancey Railroad describes some of the day-to-day operations in the WWI and 1920's time period, where they would indeed leave a freight car on the main for unloading by a nearby business, with the understanding that the business was to have the car unloaded or loaded and ready to go by train time tomorrow.  The car to be spotted would be put at the end of the train and just dropped in place and blocked there, then the train the next day would come along and push it back up the line.  Clearly, problems were presented if the business did not complete those tasks in time and this did involve the pushing or pulling of the "drop" in front of the locomotive to get it to a place to form the train into a more conventional manner.   

A SMALLER LOCO HAULING A BIGGER LOAD THAN A LARGE LOCO
South Australian Railways had two loco classes, the 800 class of 1956 and the 500 class (1964) both of which did shunting and transfer duties and some mainline duties in South Australia. The 800’s were mechanically similar to the English Electric Class 20’s while the 500’s were a home grown 500HP shunter using EE components, lighter and of 500HP but they could pull more tonnage in some areas than their older cousins and were rated by working timetable to do so.
So if one of your smaller locos can handle more than your mainline power, there is at least one prototype I know of!

DIFFERENT BOGIES ON FREIGHT VEHICLES
In Australia, there were three bogie exchange centres where vehicles were left intact but gauge changed at those Break of Gauge stations so it was not unknown for a freight car to be for example South Australian with one Yellow Western Australian Railways bogie and a Blue New South Wales Railways bogie. Although the bogies were usually matched pairs. it was also possible for them to be of different types entirely.

DIFFERENT BOGIES ON PASSENGER VEHICLES
South Australian Railways had a fleet of Railcars known as “Red Hens” on the suburban network which had two distinctive bogie types. After overhauls, it was common for these cars to have one bogie of each type as they were fully interchangeable.

DIFFERENT BOGIES ON PASSENGER VEHICLES

Canadian National had one Budd Car that had outside Disc brakes but it has been photographed with a mix of its regular truck and a standard inside brake truck presumably when maintenance was required.

DIFFERENT BOGIES ON PASSENGER VEHICLES
The Southern Aurora was a train jointly owned by the Victorian and New South Wales Railways and two thirds of the cars were fitted with NSW "preferred style" bogies while the VR owned ones had Commonwealth Bogies, the proportion being approximately the proportion of distance covered in either state between Sydney and Melbourne.

WANT TO NAME YOUR RAILWAY AFTER YOURSELF?
There is nothing stopping you of course… many railways are named after the area they serve such as Buffalo Creek and Gauley in Virginia, Central of Georgia, Southern etc but there are rail providers in the world such as CRT (Colin Rees Transport) in Australia and RJ Corman Rail Services in Kentucky.  RJ Corman even have a steam loco which they run a dinner train with, a Chinese built 2-8-2 built circa 1990. Check out https://www.rjcorman.com/

HEADLIGHTS ON ALL THE TIME
After a number of vehicle train collisions circa 1965, it was mandated that all trains on the  South Australian Railways would only be moved with headlights burning so consequently the only time a loco was less its headlights being on was in a maintenance depot, facing another loco when crossing at a passing siding or entering a terminus. It was adopted fairly much Country wide apart from the inner suburbs of Sydney.  North American locos also did this as well as using “Mars LIghts”, sort of an ambulance gyra light of red and yellow.

ONE SIGNAL PROTECTING A NUMBER OF TRACKS IN A YARD
At Tailem Bend in South Australia, trains would be re-marshalled after having gone through the Adelaide Hills with relatively lighter loads. Eastbound trains for Melbourne and Mt Gambier of an evening would line up in one of 4 possible departure roads governed by one lower quadrant signal before the ladder of points joined the main line. So if you are short of cash for a working array of signals for a similar area of your layout…

CUT DOWN LOCOMOTIVES
Penn Central took one of their magnificent GG1 locos ( a 2-C-C-2 electric) and cut it into a half unit for shop work at their Wilmington shops for snow clearing circa 1969.  I saw this unit in the flesh while passing by (incidentally riding in another GG1 on the Washington Bound “Montrealer”).

BRANCHLINE LOCOMOTIVES ON MAIN LINE PASSENGER TRAINS
I was a travelling Technician on the Indian Pacific in 1975 between Port Pirie in South Australia and Sydney.  It was quite common for NSW 47 and 49 class locos to be attached as trailing units behind Mainline units on this train. On one occasion the 47 class (Caterpillar powered 1000HP units of the time) led the train, more than likely as they were a very smooth riding unit on rough track!

BRANCHLINE LOCOMOTIVES ON MAIN LINE PASSENGER TRAINS
Up to about 1972, the Indian Pacific was hauled by 600 and 830 class units (1800 and 950 HP Alco locos) working in tandem together and did so until the arrival of the 700 class diesels in late 1971 where the doubleheading was no longer considered necessary.

BRANCHLINE LOCOMOTIVES ON MAIN LINE PASSENGER TRAINS

A friend of mine in New South Wales recorded unit 48165 ( a  950 HP Alco loco similar to the SAR 830 class ) on the front of the Sydney Melbourne Southern Aurora circa mid 1973.   I also rode back in my technician days on the Indian Pacific behind a 44 and a 49 class while on one of my weekends off, a 44 and an 830 class on hire to New South Wales worked the Indian Pacific between Parkes and Broken Hill reuniting it with some of its sisters in Broken Hill Loco Depot.

OVER POWERED TRAINS
Union Pacific did not often double head its’ bigger power, especially Big Boys in the steam era but double heading was not unknown due to power balancing purposes.  A friend from long ago witnessed 12 Union Pacific Diesel Locos including a number of their high horsepower unit  hauling a Solitary Caboose in the 1960’s, no doubt for similar balancing purposes from one end of the Wasatch Range to the other.

OVER POWERED TRAINS


South Australian Railways often had to shift power from Pt Pirie to Peterborough 75 miles east as there was more traffic on the Transcontinental line from Sydney to Perth rather than the other way around. One driver in particular hated having dead locos on his trains so it was not unusual for him to have 5 or 6 locos running on his relatively light trains with empties returning to Sydney, 3 or 4 of which were supposed to be dead hauled back to Peterborough.

OVER POWERED TRAINS

I took a photo of a Victorian Railways triple B class  on an up Dimboola passenger  in 1981, no doubt a power balancing issue as it was only 4 or 5 passenger cars behind them.

A Victorian Enthusiasts Special in the early 1980's triple headed 2 R Class and a D3 class between Bacchus Marsh and Ballan.  Really speaking, it seemed only the second loco was powering the whole train! Since that time there have been a number of double, triple and even a quad header train!

DISPARATE COLLECTIONS OF ROLLING STOCK
Where I now live, there is a tourist railway called the Bellarine Peninsula Railway that has locomotives and rolling stock from Tasmania, Western Australia, South Australia and Queensland Railways that would not have met in real life. The main train consists of Tasmanian passenger stock and I have seen it hauled by their ex SAR  T class,  ex QR PB class and an ex WAGR V class as well as their Tasmanian engines, 3 diesels, 1 steam engine and a couple of railcars.
Tasmania did buy a couple of SAR T class in the 1940’s but the others are quite atypical but prototypical!  And who said their trains shall not meet?