Will taking prozac (fluoxetine) change my brain forever?

No: Taking antidepressants, such a prozac, (fluoxetine) does not change your brain, .

Maybe: It is thought that it is the resultant response of the brain to increased serotonin levels (and not simply increased serotonin alone) that leads to improvement. Examples include changes in number of eceptors or increased number of dendrites. These positive changes may remain after the medication is stopped. If your brain was not changed from a depressed state, you'd remain depressed.