Read Starswarm (c 1985) by Brian Aldiss.
It's about genetic mods specific to colonization.
Anything from teeny tiny water humanoids to methane breathing humanoids.
I own a copy as pictured in the below.
Don't remember if I repurchased it on EBay in the late 2000s
or if it's the first (only) copy I bought.
https://www.goodreads.com/book/show/1567240.Starswarm