I looked into the hardened runtime a bit and it looks like most things can be turned off. For example, firefox is building with it according to this:
https://bugzilla.mozilla.org/show_bug.cgi?id=1470597
Here is the firefox entitlements file:
https://d3kxowhw4s8amj.cloudfront.ne...7a/D27396.diff
Basically looks like adding that entitlements file and calling codesign with it should be all that's needed (and adding the enable hardened runtime flag to Infoplist)
But I have to say, Aple's documentation is horrenduous.