[pianistslogic]

I think it'd be best to just transpose every capitalized letter between square brackets, as well as every first letter after the opening square bracket.

Following the opening bracket is a note name, conventionally written with an uppercase letter. The chord quality and extension are written in lowercase. It is the note that gets transposed, the rest remains unmodified. So `Aglibberish` becomes `Bglibberish` and `Astronomical` becomes `Bbtronomical`.

When a chord has a bass part, indicated by the slash, the slash is followed by another note name that is transposed accordingly. `G/B` becomes `A/C#`.

AFAIK there is no reason to include uppercase letters in the chord name except for the note names.

There is, though. In your example, try transposing [Astronomical/C]. It'll fail to transpose the C.