Huh? I'm not sure I understand your question.
DirecTV DVR service and Tivo service are totally independent of one another .... DirecTV provides their DVR services, while Tivo provides the service for standalone Tivos. So you can't really "bypass" the DirecTV/Tivo and swap it with your new standalone Tivo. You'll have to activate the new Tivo with Tivo, then contact DirecTV if you want to deactivate the DirecTV DVR. Realize, however, that your standalone Tivo will need a standalone DirecTV Receiver as a tuner .... it won't be able to control channel changes on a DirecTV DVR.
Sony SAT-T60 120GB (v3.5b)
HR20-700, HR20-100, HR21-200 HD DVR
HR10-250 HD DVR 400GB (v6.4a)
H21-200 HD Receiver
R10 DVR 160GB (v6.4a)