What's to stop Romney from amending his tax return after the election?

A reader writes:

Don't forget, like anyone else, Romney can file an amended 2011 return after the election and get back that 9% rate he surely believes he's entitled to. 14.1% my ass.

Meaning Romney can still get that 9% to 10% tax rate he gave us this time around for appearances.

The NYT agrees:

It is possible, however, that Mr. Romney could still deduct the unclaimed amount of his charitable donations in future tax years, experts said.