Salem

Will destroying mine support cause collapse if all area protected by that support is covered by other supports? Are there any safe ways to remove unneded support?

currently you can safely remove supports, as long as they were not built directly under a cave-in.
I.e., if you build supports before any cave in is happening, you can safely remove it afterwards.

Well, most supports that placed inconviniently are those that I've placed under cave-ins. That's bad.

Indeed, The idea is that you should build support preemptively. Those who wait for the cave-in to THEN build their supports sacrifice the luxury of where the supports go.

well, you can remove it. let the cave-in happen. put your minesupport where you want it. remove all walls except for the one unter the cave-in.