HD upgrade on unit under warranty, Tivocurrent policy?

Hi - I got a Roamio 6 mo ago and took the 3-yr extended because it was very reasonably priced. I'd like to drop in a 2-TB drive though. I had read somewhere that TiVo can tell if you upgrade, but that they were now cool about this? Or, specifically, that if my unit died and I stuck the old drive back in, they would honor the warranty?

Can anyone comment on this? It is a pipe dream, unofficial policy? Official policy? If it's not cool I'm not going to do it (I don't need the extra space that badly, - just a "nice to have").

Thanks!
/j