Like TheAlchemist was trying to say, you can change all the skin files of one weight-class to the same skin, and you will always spawn with it. The downside to this is so will everyone else.
I did do something similar. Took the Navy skin for the outrider and copied it numerous times. Placed the copies in a folder on my desktop and changed the names to the ones matching the insides of the player skins folder and replaced them. If you did that, but before the copy, change the look, i supposed it would work.
I have seen alot of people asking if they can choose the player skin. So I found a way to do it.
It is pretty simple all yo have to do is :
1. go to your legions overdrive folder and go to this path:live-legions-data-shapes
now the next folder deepens on what you play:human for raider, human_heavy for senitel,human_light for ourider.
2. choose body and now you see a bunch o files