You can and should design for change, within reason, because all successful programs will need to change in ways you cannot predict

You’ve yourself here. You can not predict how it wull change. Which means that whichever design for change you’ve made, may just as well completely miss the future utilization

Which doesn’t mean that we shouldn’t design for change at all… Just saying.

Maybe Slimbook? I haven’t bought one yet but it’s definitely on my close watch.

https://slimbook.es/en/

You have to make it easy on yourself and just use a switch with default true for evens, then gandle all the odd numbers in individual cases. There, cut your workload in half.

Could you not?