That should be fine. Per standard feat-swapping procedure: make sure the feat you intend to replace it with is one that you were eligible for at the level you took SF: UMD (which rules out Imp Crit, and I don't think the game will let you take Greater Spell Focus at 3 if your Spell Focus isn't until 6).
Another option:
1) Toughness
3) SF: UMD
6) Maximize
...
Same caveats as before, but this way you can "get away with" not taking Spell Focus if you want.