Health monitor query

I have not had an issue when reconfiguring health monitor requirements on a pool. As you are proposing to move from "All health monitors" to "At least one", i would hazard a guess that both your monitors are successfully passing the checks.

If you have doubts, you could create a "dummy" pool (and vs if required) and apply both monitors with the "All health monitors" requirement configured, then change to "At least one health monitor" and monitor to see what happens in your particular environment.