I've 'discovered' that I can increase the mains pressure to my
taps in my house by opening the valve next to my water meter a
bit further.

It will have no effect on the integrity of your combi. Although your combi
might only be rated for a particular static pressure, opening or closing a
valve won't affect this at all, it will only prevent the pressure dropping
so much when a tap is opened. Open the valve with impunity. However, if it
is a gate valve, never leave it wide open, or the valve may seize. Just turn
it about half a turn closed again. This won't affect the flow much, but the
valve might still work when you need it.

Christian.