Changing Altmemphy Clock Frequency

Is it possible to change the DDR2 high performance controller II with AltMemPhy clock frequency without having to do edit the Altmemphy megafunction and then regenerating all the files again?

I thought maybe editing the altmemphy PLL in the megawizard would work but of course the timings will be off if I change just the PLL frequencies.

How should I go about it? I needed to change just the clock frequencies without having to regenerate all the files.

Thanks