I don't think this is related to GP import only, but a more general issue

I wanted this exact behaviour recently - to transpose just the chord symbols and not the notes. If it's agreed just having chord symbols selected and applying a transpose should cause this behaviour I'm happy to look into it. As @Jojo-Schmitz mentioned it's not GP-specific.

(I'd actually like to be able to even just use cursor keys to do chord symbol transpositions, but I can see that would be problematic because they're already needed to change the vertical positioning)

just having chord symbols selected and applying a transpose should cause this behaviour

This would make sense to me

Me too. The only slightly awkward thing is managing the dialog - what should be grayed out, whether any wording needs tweaking.

Nope, it's simple, just need to change the dialog so you can access that option to transpose chord names depending on whether there are chord symbols present (in fact, it would be perfectly safe to simply always allow that option, but I figured it made sense to disable it if you've only selected notes).
One thing though: assuming the chord symbols are attached to v1 notes, you can't select a range that ONLY includes chord symbols but not those notes (even using the selection filter), so you can't use some of the options like transpose to a particular key. However you can exchange just the notes into v2, while leaving the chord symbols in v1, then you ARE able to use the transpose dialog to transpose just chord symbols to a particular key etc.

I’m not saying it’s hard, just that it would presumably requires design work in the dialog, which means it’s not just a simple code change but has that additional complication. But if you’re saying you tested all possible combinations of selections and found the code already handles them correctly without the need to change anything else, great!

Yes, it works fine. But unfortunately my suggestion of moving the notes into v2 in order to be able to select a range that doesn't include the notes doesn't work - it still transposes the notes too, despite them not being selected. I don't know if that's worth fixing too, or reporting separately.

@wizofaus @cbjeukendrup the solution is just a step towards to the main issue fix, so I'd not close the ticket

How so, what's the further fix required?

As described in the summary, the problem is it's not possible to transpose chord symbols separately from notes and wise versa. Seems it should be designed as another transpose option.
@oktophonie please, confirm or describe your plan

But that's exactly what I implemented! You can select just the chord symbols and transpose just those.

May be @abariska means adding new option in transpose dialog "Transpose notes" above "Transpose chord symbols" option.

@wizofaus your fix works as expected technically but in context of the current Transpose dialog it looks as a hack with the same list of parameters as used for notes.

• 'Transposition to key' option is blocked
• 'Transpose chord symbols' option is present and still affects to the result (e.g. if I apply transposition to selected chord and the checkbox is unticked, there will be no changes). Which is weird.

Temporarily it can be like this but the dialog should be re-designed a bit.
@bkunda please take a look, just fyi.

"Transposition to key" only works if you select a range, which has always been the case. "Transpose chord symbols" should be disabled if you have only selected chord symbols, if that's not the case then I agree, it should ideally be fixed, however this dialog is slated for replaced with a QML-based one, so at best that's a "nice-to-have". Either way the issue as stands "chord symbols can't be transposed separately from its whole measure" has been fixed.