As it turns out, fixing a reskin is not a lot easier than making one from scratch, but anyways we're here now.
The GP38-2 from Pennisula Corridor might be a closer match for the INRD ones regarding the exterior, but I chose the CSX one because I think the sand patch grade environment is closer to the real environment where these trains run. Might make a copy with the UP one though.
Thanks @KCRC_Railway for copying the file so that I don't have to start from zero again.
This reskin is also available on CC.
Install with TSW3 Livery manager.