modifying polys in premade clothing?

I've got a premade t-shirt with materials etc. and I'd like to add some wrinkles, folds etc. to it.

I'm comfortable enough in Hexagon & working between Hexagon and Daz to make the modifications I think but the catch is that the existing polys don't line up in such a way to enable me to get the sort of detail that I want.

I would subdivide the existing polys and manipulate them but I've learned enough to know that this will mean that from Daz's perspective I'm now working with a whole new mesh and not a morph for an existing mesh and that the existing material presets for the garment won't work any more either.

So my question is - is there an "easy" way to re-use the existing material presets if the additional polys don't radically alter the original mesh?  I'm guessing that what I'd need to do is unwrap the new mesh in the same way as the old mesh was unwrapped so that I end up with roughly the same UV - but to be honest I don't really understand what "unwrapping" entails and beyond believing that a UV defines the relationship between the polys and the pixels in a map I don't really understand how one would make or modify one.

Can you offer any advice?

PS - I'm OK with the advice being "there is no "easy" way to do what you are doing - if you want to add \ remove polys then you just need to remake the materials from scratch".