It used to be for the CC3 base characters that you can send non-T poses to Zbrush via GoZ. Now that option disappeared, and it seems to be only a thing CC3+ characters can do. I don't see why you removed the option for non-converted characters. Especially since there's no easy way to batch convert embedded morphs and custom expressions that old CC3 avatars already have (as the conversion process bakes the morphs)