But how would it work? Would it always open the global swing settings? Would it open the per-pattern swing settings when the pattern editor is focussed?

I didn't think of that. Perhaps it might be easier to just have separate commands/key bindings for each one?

In the case of the per-pattern swing settings, I suppose it might also make sense to enable the "Override song signature" checkbox if you select "OK" after making changes.

In the case of the per-pattern swing settings, I suppose it might also make sense to enable the "Override song signature" checkbox if you select "OK" after making changes.

That's backwards, because you first need to enable "Override song signature" before you can actually edit the per-pattern swing settings. Or were you able to edit them without checking the override box first?

It is backwards and no I was not able to access them without checking the override box, but you asked how this would work and I was just contemplating some way you could have a command to access the per-pattern settings directly since normally the checkbox has to be enabled first as you say.

My idea is currently to let the shortcut always open the global swing settings.
Rationale: When modifying these settings, you are most likely already in the pattern editor, so you could almost never reach the global swing settings reasonably using this shortcut. Per-pattern swing settings can already be reached through another shortcut (Pattern Properties).

An alternative solution would be to open the global settings if the currently edited pattern doesn't have per-pattern swing settings yet (or if the user is not in the pattern editor), and open the per-pattern settings otherwise. However, I am not sure if this is more or less confusing that the first proposal.

The second solution seems logical to me, but I can't speak for anyone else. Although my guess is that most tracker users are somewhat more technically inclined than the average user so it shouldn't be difficult to grasp.

r8692 adds a new shortcut, "View Global Tempo Swing Settings". If modern tempo mode is not activated yet, it will warn the user and open the song properties dialog instead.
For pattern-specific tempo swing, there is already the possibility of using the pattern properties shortcut, as discussed.