Locke to Gogo?

I would suggest you take a look at the event script and look for what event bits are set when Umaro joins the party and is available.

Why, you might ask? My suggestion is this: If umaro possesses steal in your hack, you need to set the event bit related to "Umaro is available" Right before locke's scenario in south figaro. This way, when Locke is put in the party, I believe steal should be an assignable ability.

Of course, when locke's scenario is over, you need to make sure that Umaro is not available anymore to the party (by clearing the event bit).

And this might bring a small issue while you're shopping in stores: Umaro might be seen in the bottom window of the character roster.