Remove and reinsert cable cards

I've had a TiVO of some sort since they've been available. I've replaced a few hard drives, gone from series 1 to 2 to Premier. So here's the deal:

My parents have a series 3 HD with Comcast. They recently upgraded their channel lineup with some new deal with a lot more channels but none of the new channels will tune in on the box; the old channels are still there.

They called Comcast and the rep told them to remove and reinsert their cable card(s). I'm not sure if they have one card or two... They weren't sure what the procedure was to do this so they have me coming over to do it.

First: is this going to work or is the CSR just talking out their butt?
Second: do I power off the TiVo before removing the card(s)?
Three: will the card(s) have to be repaired with the TiVo?
Four: any other thoughts???

Thanks in advance

MMG