Have a way for a stage's song to be permanently changed

[yamorix]

Is your feature request related to a problem? Please describe.

A feature I have been trying to replicate from an older build of my full game was for a boss character transformation. In p1's decisive round against this boss, the boss will transform and the stage BGM will change. None of the current features can properly accommodate for this change since PlayBGM restarts the stage BGM between rounds, and final.music in the select.def or stage's .def will only trigger for both characters respective final rounds.

Describe the solution you'd like

All I really need for this feature to work is for either:

1. Songs played with PlayBGM to have a way to persist between rounds
2. Have some other way to change the stage's main BGM permanently.

Additional context

No response

Search terms

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[potsmugen]

Sounds like a job for ModifyStageVar. But without string support I'm not sure how much work it'd be.