Is it safe to use indicators that only work "locally"?
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In other words, yes it is fair to use "quetzal" for Q if the crossword has a Game of Life or cellular automata theme (preferably with the fact that there is a theme called out somewhere). The solver is primed to be thinking in that direction. Thus using "locale-specific" terminology is fair. Or, you could indicate the context within the clue, for example with "Conway's/Dave Greene's quetzal".
However, solvers would probably riot if you tried to use something that specific in a standard crossword as a one-off with no warning.
As an example, see @jafe's cryptic crossword Never fear, Friday's cryptic is here! (specifically the instructions; I'm not going to spoil the answer).
Nineteen thematic answers have "in-universe" definitions. For example, Scrooge McDuck could be defined as "famous billionaire" rather than "Disney character".
The definition "famous billionaire" would be unfair for "Scrooge McDuck" in a standard crossword. But because it is explicitly indicated that this crossword has a theme, and themed definitions are to be expected, the crossword is fun instead of unfair.
What counts as a "local" clue requiring extra indication is occasionally a judgement call, and some things that I might consider absurdly "local" (e.g. British military terminology) are simply accepted as "normal" due to cryptics' UK roots. Making clues clearer and more unambiguous would never go amiss.