Hey Paul! So, just to clarify, if Bob wants to explore lineage B, they can just have the one TM cast to go straight to lineage B - they don’t need to have lineage A stripped off first, unless they’re trying to permanently change lineage (which it sounds like is what you’re interested in!).
The TM page says that although you get light roleplaying effects from your “new” lineage, you don’t get the boon from it, implying that it’s more of a glamour than an actual change of lineage.
Although the TM page doesn’t say that you can’t use ilium to make it permanent, the lineage Wiki page states:
"It is exceptionally difficult to change lineage - even more difficult than becoming lineaged if one is human. No known magic will reliably change lineage - in the rare occasions where it has been achieved it first requires the person to lose their lineage, becoming fully human, before gaining a new lineage via the normal (arduous) process.
Becoming lineaged, or removing lineage, are both significant goals your character can accomplish in play, but they are likely to take time and effort to achieve, and success is by no means guaranteed."
Which to me implies that it isn’t as simple ilium-ing a TM, especially as it says success isn’t guaranteed. I would recommend dropping an email to email@example.com as they’ll be able to officially confirm this either way, and possibly get the TM page updated to make it clear in future!