since my question was deleted and not answered (Entirely prevent specific apps from starting), I'll post it once again. Reason: Problem still exists and I found a (workaround) solution. So posting it again with the answer might help others with the same problem.

Here it goes:

I have a certain issue with my Mac, which is that in certain situations, "standard" system apps are started. For example, clicking on any link in MS Office will fire up Safari, which I never use while my "normal" Browser is configured as "default Browser" in the system's settings. Connecting a BT headset will start Music, which I never use.

As it appears, there is no way of simply "deactivating" this behavior. As there is apparently no way of "patching" the system by completely uninstalling system apps, I want to at least prevent them from being started.

What I want/need is a way to force-stop specific apps (quietly) as soon as they are started. Like watching if a specific process is started and immediately killing it.