I’m afraid I can’t find a workaround for this. In a piece in 2/2 I’ve set the initial TS to 2/2 and I’ve added a hidden 4/4 TS in bar 2 so that the beaming is correct. Unfortunately this breaks MM rests in the parts in which an instrument doesn’t play in at least the first two bars. Is there any way to create a proper MM rest without having to remove the 4/4 TS and change all the subsequent beaming manually?
No, but here’s a better solution: Trick Dorico 3.5 into beaming and grouping 2/2 like 4/4 - YouTube
Then you can’t use the substituted symbol anymore elsewhere in the piece. But it’s always good to have several tricks up your sleeve.
My solution would be to put the hidden 4/4 at the earliest point where it doesn’t break any multirest: rehearsal marks, key/tempo changes, any sort of special barline or simply a tutti, and re-beam/force duration until then. Much more low-tech than Leo’s solution, up to you to decide which way feels less “hacky” I suppose.
Thanks to all for the solutions. It is indeed good to have several possibilities. Let’s hope that these workarounds won’t be necessary in Dorico 4!