Frames cannot be enabled or disabled via Edit Text Style
- Add a rehearsal mark to a score
- Style > Edit Text Styles > Rehearsal Mark
- On the "Frame" tab there is not an option for disabling or re-enabling the frame
As a workaround you can set the frame color to white, or edit each text frame individually via F2.
First reported by Micbass3000: http://musescore.org/en/node/1667