Instead of forcing users to select a new font during font substitution for missing fonts, allow some temporary font to be used for the duration of a session, without changing the underlying font itself. This way you can work on a file on a machine lacking the fonts without fear that the underlying fonts will be changed.
I switch between computers a lot, one is a Mac (my primary music-making-machine), the other Windows. Some fonts are just not available on Windows, or even when there’s a valid substitute it may not be recognized automatically as the same font, so a font-substitution dialog would be useful (Note: there is such a font-substitution dialog, but it doesn’t appear in all situations, see my comment on /t/font-substitution-warning/128781/4 ). So I would like to be able to edit a file with missing fonts without fear that the missing fonts will actually be replaced with some other font - but it would be great to be able to choose a temporary font to use in its place for the duration of the session (ideally, this could be configured via some global preferences even, so I don’t have to make the same selection every time I open a file).
Please note that as things are now, if I use Windows to open a file that I last saved on my Mac with some Mac-only font, I am not even presented with the option to substitute the font because these font changes weren’t done via Paragraph styles or Font Styles.