FASA Games, Inc.

Could a group pattern item be upgraded to Major or Core?

By the rules as written - no.

At your own table - absolutely, if this is what you want.

Yeah, group pattern items inhabit a strange kind of middle ground. They are treated kind of like minor pattern items in the sense of the maximum rank thread that can be attached to them (Rank 5), but unlike minor pattern items they can have 5 different threads attached (instead of the one normally allowed for minor items). That, incidentally, is the same as a core pattern item, so...

Group patterns are pretty robust and powerful as they are. How would a "Major" or "Core" group pattern item manifest? Is it only allowing higher rank threads, or is it expanding the power in other ways as well?

It's an interesting theoretical exercise... but kind of scary.