Sounds like Decal Master might be want you wish. Basic steps are:
a) Load Figure
b) Load texture
c) Add ‘overlay’ image(s)
d) Save texture with new name
e) Back in DAZ, apply new texture
I tend to save the new texture (ensuring a new name) back into the original MATpose directory (easy to do with Decal Master). You get an icon based on the original, with a Decal Master logo in one corner for the new .pz2 file.
Decal Master handles all the issues of cross seam boundaries and permits orientation, position and size manipulation.