Link layout changes to score/parts

Accidentals are certainly content and are certainly synced between score and parts.
Not so sure about brackets. You say "might", Wich already indicates that these may be different at times. The syncing is all or nothing though, so we tend to not sync in case of doubt, as we can't 'break' the link currently

You need to add brackets to score before creating parts.

(So sometimes you would need to remove parts and recreate them).

EDIT:
Whups, I missed, it is feature request. It would be nice, I agree.

Fixing this should be a simple 1-line (1-word actually) change, from

      { Pid::ACCIDENTAL_BRACKET,      false, "bracket",               P_TYPE::INT,                 DUMMY_QT_TRANSLATE_NOOP("propertyName", "bracket")          },

to

      { Pid::ACCIDENTAL_BRACKET,      true,  "bracket",               P_TYPE::INT,                 DUMMY_QT_TRANSLATE_NOOP("propertyName", "bracket")          },

In libmscore/property.cpp, line 137 in 3.x resp. src/engraving/libmscore/property.cpp, line 160
But a) as mentioned, this would make it impossible to have it different between score and parts, so I'm not sure that's the right thing?
and b) for some strange reason it doesn't work, so is not that easy apparently...