Hello.
Is it possible to regulate the Volue of a Sound/Music Zone?

If yes, how can i do it?

You can alter volume with Lua commands so I imagine just can make your own amended script for the zone to set the volume when you enter the zone. I'd probably make a trigger zone with the said lua script attached rather than use the standard music zones. Or add an object with a distance range where it plays the music when you are close enough. That is how I got all the music in Commando working, and how I triggered the mid boss music. The game is available still on the Showcase section, so you can try that and check out my scripts.

There's no way to do it without some kind of scripting as far as I know at present.