Modifier to add a new default to a Skill

[Engurrand]

I'm fairly handy with the GCA but I've run into something I just don't know how to do. I often edit skills to add relevant Wildcards as entries to the default tag, so that the component skills of a wildcard can be bought up above the wildcard level. Since this kind of editing is fragile, I'd love to do it properly with a skill modifier, however, I haven't a clue how to create such a thing. Is it possible? Can anybody help me out?

Cheers, and thanks for an amazingly helpful program.