I meant the editor was bugged for me. When I opened the editor after making an offspring, it would display the points I have ammassed during gameplay but after purchasing a part, it would reset to the value you get at the beginning of the game, so improving your creature was impossible. I think this was a bug and not intended.
But maybe it as already been fixed because I haven't played since 50 days. Still, please playtest again, gain some DNA points, try to customize an offspring with those newly gained points and see if it works.