Hmm...so I guess we won't know how it really goes until your renewal date rolls around. I was curious because I know that if you upgrade your pass, Disney says the new level and any associated benefits don't kick in until the first day of the new pass. I was concerned that adding max pass on a renewal might somehow screw things up, and that it would in fact expire on the original expiration date and not the new renewed pass expiration date. That would really tick me off. I don't particularly care if I get the benefits before the actual renewal date since I am more likely to renew online and not return until the new start date anyway.
The thing that does tick me off about Disney though is that they tell you that if you upgrade, that your new benefits won't kick in until the date of the upgrade, but I have noticed that if you downgrade during your renewal window, you immediately are converted to the lower level pass and subject to whatever limitations that imposes. Technically I haven't tested out how true this is, but when I renewed last year from a Signature Plus down to a Signature my online account through all portals, computer and app, showed me as having a Signature pass with blockout dates, etc. a full 2 1/2 weeks before my original expiration date. For me this didn't matter, but I can see situations when it might for some, so it annoys me that they "penalize" you in this way for renewing early.