Is it the same for BrawlBox v0.67b.zip? That's the one I have.
That would be a definite yes. I don't know when it was first implemented, but it seems likely that it would have been one of the first, since costume "vertextures," as Mikuru calls them, were among the first kinds of hacks. So the main reason we create both .pac and .pcs files is to prevent freezing on transforming characters and allow them to be used in single player modes.