A 278 No.
You can't switch the grid intersection for a spell after casting, whether that grid intersection is a point in space or centered on a creature.
The answer for the most part is that you would continue to benefit from your class abilities but would be unable to advance in the class until you satisfied all requirements again (because Step 1. Choose Class happens for every level advancement; see Player's Handbook on page 58). The exceptions are prestige classes in Complete Warrior and Complete Arcane. These two books have rules which strip class abilities if you fail to continuously meet their entry requirements. The two rules are substantially different; see pages 16 and 17 of those books, respectively, for the details.
For feats, you immediately lose the benefit if you do not satisfy all prerequisites, and regain the benefit as soon as you again satisfy all prerequisites.Level Loss
A character who loses a level instantly loses one Hit Die. The character’s base attack bonus, base saving throw bonuses, and special class abilities are now reduced to the new, lower level. Likewise, the character loses any ability score gain, skill ranks, and any feat associated with the level (if applicable).