You do need to remove the scope to adjust the barrel. There are 3 grub screws in the top of the action and i think at least 2 are under that mount.
I really wouldnt worry about the barrel adjustment. I've had the rifle over 2 years and used it a fair bit. The only reason i took the barrel out was I wanted to. I take *everything* apart, so by about month 2 i took the barrel out to have a look. No need though and it hasn't been touched since.

I did read on here someone had trouble with the mags, the had 5? mags i think one was too tight and adjusting for it made the others too loose. I've not had that issue though i suspect you could exchange a mag that isn't working. they're €40 each and made to a very high spec so should be replaced if they're not working out.