Adding to the above....
I just posted a couple of custom paks here.... viewtopic.php?f=74&t=2389
These are pk4 files that once TM is set up right, will allow for greater customization of scenarios. In this set, I have made all the locos and express cars match under the fictional Persian Star Railway. Included are mosques to replace churches, and sounds to make things eastern.
These files can be used when playing Persian Electric to give the scenario a bit of local flair, and at the same time alter the way the cars look in the game.
TM was designed to make customizing easier, and a development kit is available. It's possible to make a little, or a lot, and thus when creating a scenario, it will be possible to customize it. I do expect that I will most likely make a lot of the content for this, but it is open to anyone who wishes.
For the CNR scenario I am planning on, my goal is to have a complete set of cars and locomotives appropriate for the time and place for use in this scenario. I may even go as far as to make some freight cars too. This way, when playing the scenario, all the cars will be for the CNR.
In addition to custom sets, I have some full car sets coming, so there will always be options of sorts when playing scenarios.
So this can be taken into consideration when creating scenarios. Of course, if it seems to big a job to tackle, but you like the idea, I can usually be persuaded to help out and assist making custom paks to go with scenarios.