Well, you can use smaller ones, just more of them. Capacitance value is additive. Two 330uF caps (660uF total) is the same as three 220uF caps. It's actually better to use more caps as it spreads the heat out a bit and each cap doesn't have to work as hard. As long as you meet or exceed the original total capacitance value, you're ok. Unless you are like ZeroPointBug who decides to solder a bazillion caps on his ESC.
