You can apply the old V4 .cr2 in the setup room and then save the character. Important that in your initial export you check the include group names in the export dialog.

If you're doing extensive morphing of the whole body, it's not a bad idea to grab Compose, which is a freebie utility, that allows you to weld all duplicate vertices together and then rebreak the groups properly after the morph work is done.

It's doable and fairly simple.