Dynamics - CUstomize on a flow basis

For my first experience using flows I am notating a multi-movement piano piece with one flow per movement (seems logical enough). The first & thrid movements are highly percussive and I want the accents and marcato to be very strong (I’m setting them to 2.0 & 3.0 respectively); but for the middle movement I want these to use the factory settings.

AFAICT there is currently no straight forward way to do this - I guess I could apply mp or p on the accented notes in the middle movement and hide those, but that’s really kludgy - it would be easier to split this up into 3 files.

Am I overlooking something?

You are not. Engraving options are applied to the whole file, not to a flow — Notation options are on a flow basis.
You might (I have never used this new editor myself, so I’m just making assumptions here) use the new playing technique editor to create your own strong accent and marcato signs and use them where you want, and thus be able to keep everything in the same file…