From RMSS, the wording is "normally, a character can only develop one Lifestyle training package" (section 15.3) - but that's under Apprenticeship skill development section, so it would only be valid for Apprenticeship.
However, in Gamemaster Law, it is said (in section 9.2.3) : "remember that a character can only have one Lifestyle training package at a time" (emphasis mine). It implicitly indicates that you can have several packages over the course of a character's lifetime, and potentially the same one several times.
The caveat is in the technical parts of the training package description, especially the time to acquire (which can be fairly long - Vocational TPs are usually ~20 months, while Lifestyle TPs are 50+). Certain benefits (notably starting money) are only available if the training package is developed during Apprenticeship (RMSS A-6). Even developing TPs after Apprenticeship is subject to GM approval (same section, "gaining training packages later") and no TP can raise a skill above 10 ranks (there are a few exceptions that are explicitly listed).
All in all, I think there are enough restrictions to allow taking the same package several times (for some of them - e.g. Soldier, it even makes sense when you see the benefits), but the time to develop them might be prohibitive in an ongoing campaign and the 10-rank limit will quickly make that kind of development horribly inefficient.