I had a bmt 12 yrs ago if i end up needing a liver transplant how risky would a second transplant be?

Depends: The risk of transplant is primarily related to the underlying disease. 12 years out from your first transplant (BM) i assume, a solid organ transplant would be of little risk. The main issue would be in finding a suitable donor as the match may become more difficult.

Centers are doing it: So patients with solid organ transplants have been undergoing bmt and vice versa. There are papers published about case series. Yes many centers may be shy of doing it but it all depends on the type of transplant and patient's condition. It also depends on the expertise of the center