I need to write a function in my own plugin and overwrite a function from another plugin and (preferably) not make any changes to it. Or WordPress' core. So, basically, what I need to happen is: plugin X do it's work, it's time for function Y to do something, and instead of X's Y function, my function comes and do Y's job. Then X goes back to it's other functions.
I know the question has been asked before (some 3-4 years ago, when there were hooks) but any help'd be appreciated.