Cool, but everybody is moving to Gimp V3, and in V3 you have multiple layer selection natively.
Also, after a quick glance at your code:
scale+rotate can be done by chain-linking the layers (and this applies to other transforms, including move)
why are you only supporting some blend modes, and mostly legacy blend modes except add/subtract?
why are NoHalo/LoHalo not supported interpolations (OTOH I don’t see your code using the value anywhere, so it probably runs with the user’s favorite interpolation anyway)
Well, fact is I am slow
Not being able to use v3 (old pc), I did it mostly for the stuff I usually do for when I use Gimp, and I don’t use it everyday.
Glad to know it’s now available natively, so when I’ll upgrade It’ll be there.