Can I "give back" a housing allowance to my church employer. By that I mean I wish to be treated as a standard employee and receive no pastoral benefits

Sure.  But if they paid it to you in 2024 and you pay them back in 2025 then they may not be able to adjust your W2 in time.  Or be willing to if it means adjusting their books for last year.

So you may be on the hook for 2024 but you can get it changed for 2025 and going forward.

@tedinaddis