ALPLL mif flie update on the fly?

I do not get the question exactly but ...

*I guess you want to change plle settings and regenerate a programming file without recompiling? Try ECO change.

* if you really want to change pll settings while the fpga is up and running, you need manipulate the pll using the reconfig pins that can be enabled in the alt pll function. These pins manipulate the the actual pll settings that are stored in a serial configuration chain. It is not regular a memory block and therefore you cannot update it on the fly using the regular method. There are quite some application notes about this topic. I can warn you though: manipulating pll's on the fly gets quickly quite complicated...