Ok.. Here's what to do if you got a substitution for the dvd burner. I just got off the phone with a rebateshq csr and he told me to write a note and submit it along with the rebate info. Tell them that you purchased the 2x Cendyne dvd burner and Officemax substituted it with this 4x drive (how lousy of them. 😉 ). The rebateshq CSR assured me that it would not be a problem and that if it was, to call them back.
A similar thing like this has happened before. I called with a question prior to submitting my rebate. When my rebate turned up invalid, I called rebateshq and told them that one of their CSR's told me that it would be ok to submit the rebate, they then went ahead and changed the invalid status to "processing". In my experience, I've found that rebateshq is very lenient in validating rebates if you explain to them that you spoke with a rebateshq csr prior to submitting the rebate and that's what they told you to do.
Hope this helps someone.
Sal