Just got a copy of the game and noticed something. The Gene Freak awesoming up block lists several mutant schticks that don't appear in the mutant schticks section. Likewise there are several mutant schticks in that chapter that aren't listed for the Gene Freak. That seems odd since the Gene Freak is the only archetype that can even use them, so why have others?
My instinct is that the Gene Freak list has some misnamed items, and it should just have access to all the mutant schticks.
I got a similar response from Cam Banks about the Cyborg's schticks. If it's listed in "Awesomeing Up" but doesn't exist in the book, it's a mistake and shouldn't be there.
And I agree the Gene Freak should probably just get access to all the Mutant schticks, nobody else uses them.
Yeah, originally I told my player that they were probably for some kind of expansion character or something... but... I figure if he really wants one of them... might as well go with it.
It's been said that the shticks in the awesomeing up sections (that actually exist) are a curated list of options that should be fun & balanced, while the larger selection of shticks in the various chapters, some of which are not listed on any awesoming up list (especially creature and mutant shticks) are a bit untested, and may prove to be under or overpowered in actual play. Those shticks are "your millage may vary."
Robin Laws has noted that FS2 is a bit of an experiment in reduced character creation process: and I suspect the awesoming up processes is similarly curated.
If you are new to the game or otherwise not the type to enjoy fiddling with things, the game won't require much of that from you. If you are the type who enjoys fiddling with things, well look at that... there are all kinds of extra shticks just laying around in the mutant chapter, not being used at all.
Every schtick in the book is fair game for you to include. We made conscious decisions in most cases to provide a solid, play tested list of options on archetypes but as BlackJaw says, if you want to sub in those other schticks as you're awesoming up and the GM's good with it, go to town.