I wouldn't recommend Modo just for grouping. Way too expensive these days. Modo is a fine design tool for SDS work and a handful of other things, but if you do not already have it, then it probably isn't a good starting point. Tony (above) recommends Blender--I'd give that a try (notes here: https://www.renderosity.com/mod/forumpro/?thread_id=2888830). Wings and Silo are also well liked but I can't speak to the polygon tagging capabilities. I haven't used UVMapper Pro in a long time, but I think you can do you naming in it as well.

The main trick is that in general there are two kinds of polygon tagging going on in a poser .obj file. One kind of tag identifies which materials are used to color the polygons. The other kind of tag is used to identify which polygons stick to which bones. It is also vitally important that the bone tags get names so that the name of the bone is the same as the name of the group of polygons.

.obj files are fundamentally text files in their native format. You can edit them with Notepad++ (recommended, free.) Polygon groups are named by the "g" (for group) tag. The "usemtl" tag will identify the material or texture to be used. These tags can be manipulated by hand if needed. There are some tuts on .obj files on the web, but I'd consider this a last resort.

Cheers! -K