In film scores with lots of modulations it’s common to write without the key signature written at the left of each system. Everything looks like C major but the accidentals are written inside the music (like writing for french horns). I started writing ‘in C major’ but changing key signatures helps to avoid enharmonic nightmare. So is it possible to hide those key signatures while having the accidentals follow a key (i.e. Ab-minor)?
Edit: Took me a moment but I finally understood what I think you’re asking: can you set a key signature for accidentals to follow enharmonically, but not have the key signature shown and instead show accidentals on each appropriate note? I don’t know of a way to set that globally, but the filters in Dorico do include “Notes by pitch” and “All sharp notes”/“All flat notes” - you could globally select your Ab major section, select any sharp notes and turn them into the enharmonic flat equivalent?
(Depending on the result you want, inputting an open key signature (rather than C major) might be preferable, as the default behaviour of accidentals in Dorico is different in an open key compared to C major or A minor. It could be risky to write, for example, Abs without any key signature or accidental to make it clear to the players that’s what you want.
You can also check the accidental settings on the Accidentals page in Notation Options, as there are different settings available, such as the default duration rule and when/where to show cautionary accidentals. You can open Notation Options by choosing Write>Notation Options, or press Ctrl/Cmd-Shift-N.)
Yes, exactly! Sorry… my English 
That’s a good way to clear up a cluttered track already writen ‘in C’. But I didn’t know about the ‘Open Key Signature’. That’s probably the way to go when writing stuff like that! Thanks a lot!
No your English was fine, I just misread it the first time around! Glad I was able to help