Can the brace/stock be upgraded on the tread pistol. If so any suggestions

The Tread carbines use a standard mil-spec buffer tube, so the world is your oyster for stock replacement.

The pistols use the KAK Shockwave blade, I think, which uses a proprietary pistol buffer tube. I assume that "brace" can be swapped out for something that's also compatible with the pistol buffer tube. I don't dabble in those, though, so I can't tell you what your options are there.