Question regarding UV mapping
 

I wonder if you can just uv one half of a image and mirror it without some weird stretching and such. :)

do u mean mirror the map or the painting

if u mean the map and ur model is symetrical u delete one half map it line the uvs in the editor up properly
mirror geometry and merge
buth sides should be mapped without stretching

if u meaan in PS yes and it shouldnt stretch but reme if it has writing u cant just mirror it