Ooh interesting question... my gut feel from my HACCP training is "you only need to validate once unless you change something" and I will explain why this is both a true and a false statement.
Validation is basically "can it work?" so it is a process of checking whether the CCP you have designed can be effective. In a world called "Ideal world" you would be doing this before you even open the factory and before you process a gram. Where is your starting point? Well there are a couple of main ones, literature (e.g. academic papers, retailer codes of practice, legislation, kit manufacturer's validation) and there is testing yourself or by someone you appoint to test for you. The ideal validation probably has an element of both.
So for example, you are validating a cook process for some chicken. You would want to use the literature to try and find what target temperature to choose, you would ask your manufacturer to balance the oven and you'd measure it yourself for cold spots so you knew you were targeting worst case scenario, you may then datalog the cook process to ensure the chicken cooks evenly. You would do some microbiological testing as well and you'd repeat all that a few times and that would be the validation.
So the question on repeating it. Should you? Well strictly speaking Codex would probably say "not needed" as your verification tests will indicate if something is trending out of control. But is a good idea? Hell yes.
Is it a good idea to rebalance an oven on a periodic basis? Yep. Is it a good idea to crack test a pasteuriser? Yep. I suppose though all of these, in a way, fall into prerequisites because they are effectively calibration tests or PPMs which are then supported by verification data. But people often call it "revalidation". Does it matter? Nah. But I suppose what I'm interpreting your question as is "should I still check some of the parameters I checked as part of my validation?" in which case I would say "yes". It's not really validation (IMO) but I don't think that matters.
This might all seem a tad confusing. I suppose what I'm trying to say is "it's not massively important what you call it" but also "some of the tests you use as part of your validation can also be used as prerequisite tests and verification". It all depends on the frequency in my opinion but whatever you call it, repeating some of them is a good thing to do.
That's probably now really unclear... 
Oh well, I tried my best! 
