Sounds interesting and not too difficult! But look at this pic: I´m afraid to remove the yellow and sliver trim lines as well when peeling off the Scotch tape because these trim lines are so close to the lettering. And I can´t imagine cutting the Scotch tape to fit because it would be a too fussy job.
I’ve used Solvaset / soft rubber pencil eraser method on several Walthers passenger cars with no problems. After removing the lettering, I wipe the model clean with a damp soft paper towel. When dry, I spray with gloss finish, add decals, then seal with flat finish. It looks fine to me, may be you could tell what was done if you really examined the car up close but on the layout it’s fine.
Here’s a pic of an old Walthers H-10-44 that came in black paint, factory decorated with yellow lettering and stripes for the Wabash. I removed all the lettering and stripes and re-lettered it for New York Central.
Sorry for the delay in responding, but I just tried it on a newer run (hex drive motor) Blue Box SD40-2 and… it didn’t work [:(]… for me, at least. Back to the drawing board, I guess.
I just used Solvaset and a pencil with an eraser on the end to remove lettering from a caboose I’m repainting. It took about 3-4 minutes to remove the lettering completely.