For marketplace content ‘Users are free to modify any content they purchase from the Marketplace’ but for Epic’s example content there is the additional proviso that they are ‘Licensed only for use with Unreal-based Products’.
Just to be clear, this doesn’t prohibit someone from, for example, importing a model into Max/Maya/Blender and altering the UV layout to support a different texture would it? Assuming of course the modified content it is ultimately used solely in an ‘Unreal-based Product’.
Even now as I write it out is seems pretty clear cut but I’m the paranoid type.
Oh and the obligatory “I searched as thoroughly as I could and didn’t find posts and couldn’t find anything on this”. 