Simplest reply?
HELL NO.
The hardware is very tightly coupled, and ALL of the drivers for the important parts are written by Tivo themselves, and while the source code modifications for what Tivo has done are downloadable (per the software license compliance of the GPL), they can not be uploaded into a TiVo because of the software validation processes which prevent non-signed updates from being flashed into the system.
Trust me man, been there, done that, lost sanity, don't even think about it unless you somehow know of a way to bypass all the insane hardware lock-down that nobody has been able to of late.
-Thom