No, there's no real way to change what's already been mixed down into a single audio file. There's a program called Melodyne that allows you to edit notes within a mix, but it's rather expensive and it relies on the math of harmonics to do its work. As such it can't distinguish between the harmonics of the instrument your modifying and the harmonics of something else that happen to fit the same pattern; i.e. your editing affects both instruments instead of just the one.
But even there it doesn't allow you to replace what's there.
But even there it doesn't allow you to replace what's there.