So, I've never modded KSP before, but I really liked the yellow trucks. To try and get them back in KSP 1.2.1, I've hacked on the config files, and built something that actually works; albeit without the small yellow wheels. I simply removed the wheels from their housings, and created a 70% scale version of the stock TR-2L. Is it OK to distribute the resulting files?
Alternatively, I could use git to create a patch file, which others could manually apply, in order to not redistribute others' work.
Picture of resulting trucks; stock built-into-terrain version on left, modified physical version on right.