Far from a solution, but a push in the general direction, if you hex edit tivoapp at address 0x46AB38 and change it
from 41 86 00 34 to 48 00 03 F4
then it *sort* of does what you want.

The live cache doesnt get deleted, but the progress bar still thinks it has been (probably along with other parts of the system) - the first visible result is that when you change channel the 1/2 hour buffer is basically squeezed into a progress bar which is a couple of pixels wide. This means if you rewind or fast forward you either end up back half an hour or watching live tv, with very little control in between. It also seems to get angry sometimes and not let you ff/rwd past a certain point, or thinks you are at the start of the progress bar when you are actually at the end. It's possible that it also may not be deleting the cache that is older than 1/2 hour. Chances are it broke other stuff too...

So to summarise:
1) Live TV cache is not deleted when you change channel
2) Lots of stuff went screwey/got broken by skipping a large chunk of code
3) An entry point is given in the file (address 0x46AB38) to further narrow down exactly which part of the code resets the cache (instead of just skipping the entire chunk).
4) Get yourself a disassembler and start looking!