I am sorry if it can not help you,,
and hope vendor set clean uv set for the surface group,,to easy to set new texture,,,
I think basic suit is offered to customize by user easy,so need clean uv map,,, and grouping.
but if just hope to change UV map to divide two part about torso,,(not change group)
if use hexagon,, it is simply 5 minutes work,,I think,,,,
of course , if want to release the new material preset , need to provide new UV set with the surface group I think,,,
just export basic suit to hexagon,then select UV view,,
hide other surface domain without torso,
then select one face of front part in UV map,
sift and + key, then select front part only.
then translate,, them.
after adjust UV map,, then export is as obj.
In ds , on surface option, load UV map then select the saved obj.
I can toggle the UV map,, in surface tab, edit,,
then I can save the UV set as vnedor name.
Now I load the basic suti, it has two UV set,,,..
and when I toggle UV set to my made UV set, the part are cleane divided,,
then now I understand,,
the problem is we can not offer the obj with new UV set,,
I am sorry ^^; , just approve and send bug report of yours !
Click thumbnail to see full-size image