The Planets around Tau Ceti may be fairly volcanic

[Rynn]

I was going to say '2g would be do-able if miserable for the first couple generations, and the grandchildren would be tweaks...' but I can't justify less than 3g with the math, and 3g would be a whole lot more no-fun than 2g. I don't think it would be wise for a 3g tweak to retain the human bodyplan. Something more like a squat centaur maybe.

Agreed, bipedalism is hard to justify under such constraints. There's too much risk of fall damage and being upright would put a lot of stress on the vascular system. You might be able to do it walking around in a powerframe with extensive modification of the heart, lungs and probably most other organs. But if you're good enough to create aquatic humans you're good enough to make a hexapedal human that's more akin to a giant turtle than a hominid.