Jishuo Yang's page

Ah, sorry for the belated response (I rarely frequent these boards, unfortunately...), the thing is, I wasn't the guy who thought Combat Casting would be a good prerequisite feat for the Force Missile Mage anyway.
It was my original intention to include Spell Mastery (Magic Missile) as a prerequisite (I have this stigma against sorcerers. :P), however, the editors wished to refrain from restricting the FMM to one class only, so they substituted Combat Casting instead. I would wager a guess that the editors' justification would be that since the FMM is already an offensive-spellcasting class, its members should have considerable experience in casting in the midst of battle.

That said, your suggestion would be fine as long as your DM agrees with it. It is my personal opinion that Combat Casting is a waste of a feat, since the +4 bonus to Concentration check while casting on the defensive is practically useless (any spellcaster who's maxed his or her concentration skill should be able to make the defensive casting check most of the time), and with the advent of the Spell Compendium, grappling a mage successfully is nearly impossible (Benign Transposition, anyone?).

So by all means, replace the Combat Casting requirement with something else, although I would lean toward the feats in the PHB (not the PHB2) just to be safe.