I'd think there should be two different words used to describe this:
One would be a COLLAPSABLE stock, as in those illegale for post-bans.
The other should be ADJUSTABLE stock. Where tools, however minimal are required to adjust the size.
you see, i'm pretty sure that the reason why collapasable stocks are illegal (besides the scary evil name) is because they fear that one can conceal a rifle with the collapsable stock, then instantly extend it and start shooting....after all, it isn't illegal to have NO STOCK AT ALL (this may not work on ARs, but would work on AKs, Cobrays etc)
However extending it instantly is not possible if tools are required...So i believe there would be no reasonable reason to make that illegal. Do you guys get what i mean? I hope this made as much sense here as it did in my head.
IMHO