How to change software behavior based on different state laws?

I was wondering if there is a better way to handle state laws rather than if this state do this code or if other state do other code. I've heard of rule systems but my company's code base doesn't support any of them (vanilla coldfusion/lucee for the with vanilla javascript and jquery).

Switching to a new framework or language would be too much work for our small team/company. There's lots of legacy code that we can't afford to change.

Is writing our own rule management system the best way?