It was a great idea for RS to not use the huge duplication system of MSTS, however the upside of that was each route was a self contained "unit" and nothing interfered with anything else.
The worry I have is that people will install v1 of an item produced that was packaged up with a route just after release, and unknowingly overwrite the updated (and maybe fixed!) version.
RW gives a warning if you already have something installed, but as far as I'm aware it doesn't perform any date checking - I could be wrong on this?
On principle of being able to include my freeware work in routes, I've got no issues with anyone doing anything at all with any of my stuff. If I did, I wouldn't put it up for downloading in the "public domain", I'd distribute it privately. Reskin it, redistribute it, hack the files, whatever
As long as you're not charging money for it, or the product it's included in, then do what you like.
I'm not even bothered about credit.. honestly, the people I've dealt with have always been really nice and have always asked me anyway and given credit. Those who would choose not to do either would probably distribute it without permission anyway.
