Legally, any fund that tracks the NASDAQ 100 must follow the rules set by NASDAQ, so you'd want something that is neither a total market index, nor tracks the NASDAQ. Something like an S&P500 index would work
Not legally, only by contract/specification. Funds could get sued for deviating from the index, but funds generally have a decent amount of discretion in my experience in how they handle rebalancing.
What is an example nasdaq 100 fund that isn't float adjusted?
What law prevents someone from choosing to buy stocks from the NASDAQ 100 however they want for a fund?
> Legally, any fund that tracks the NASDAQ 100 must follow the rules set by NASDAQ
No? Contractually, maybe. But legally you can do whatever you want with index constructions.