I want to insert a master repeat open & closed inside a measure (I can do this, no prob), but I don't want the measure count to change.
NWC2 allows you to exclude measure(s) from the count, but NWC 1.75 does not. With NWC 1.75, turn measure numbering off and use text to number the measures.
And why would you want to do that? I can see the need for it on a hidden staff (done it myself a few times), but then that wouldn't be a problem with the measure count. It's just not done in real music.