We generally try to keep things as current as possible and also keep the community updated when something is being updated or dropped off like when we cut PHP 5.6 here.
We do have a feature request for some users requesting to be able to use older versions of PHP here as well. We’ve also seen users in the past create requests for a specific version of PHP (i.e. 7.0)
As far as “hacking” Local to install an older version of PHP I’m not sure how viable that is. I can’t say it’s something I’ve tried or have documentation to give you but others in the community may have some tricks to share. We’ll always recommend utilizing the latest PHP/WP versions when possible to maintain the best site security and performance, but we will always keep at least the last two or three previous versions readily available in the app for users to work with.
I know for using older versions of WordPress one of our users made a simple plugin here: