You would have a magazine manufactured after 1994 that was loaded with more than 10 rounds of ammunition, certainly grounds for a case even if it is a little shakey. I imagine it would be classed as a conversion in just the same way that removing the restrictor would be. I'd be surprised if magazine width and the gap on the feeding lips didn't lead to at least some FTF problems anyway. It's a bad deal whichever way you look at it, if you don't feel confident in terminating any given threat with 11 rounds of 9mm , change the gun not the magazine or carry reloads. Don't get me wrong, I think the mag ban is a sick joke, but like other sick jokes, sometimes they get elected.
Mike H