On PC you can via mods but why can’t DTG add directly on PC and consoles too a functionality to share our liveries like in Gran Turismo by exemple ? It’s a mystery but I think having heard one day it was a licence issue
An idea would be to alow the player to edit the original livery so that you could add your customisation to the original livery Eg: southeastern class 395 mask livery or train bow. Or class 377 NHS we thank you livery. This would make it easier to add these as you wouldn't have to recreate the whole livery to make these. Also weathering would look really good to as it would add to the usage and age of the locomotive. This is more of a general suggestion to the new livery editor then something that would be in the stream.
