One tip I will give you. Clone the original first, then if it goes pear shaped the original is still usable.
Ok 2 tips.
Find a loco with a shadow (in body shadow file) copy/paste to desktop.
3 then.
As above a loco with a mesh file in it's config. Make an exact note of it.
Use both the above in each loco you want to alter.
Enjoy the rapid ageing process. You'll see what I mean.