Seed sprouted from store Hass probably won't survive above-ground lower than about 23F, in Florida 8b. In my experience most survive occasional brief hard freezes (18-23F) as stumps and sprout back when it warms up. The ground is warmer and frost insulated versus the air around when it freezes, as long as the bad freeze isn't too extended.. They often survive, but sprout back with less vigor. I had one seedling grow 7 foot it's first year and put on a few branches and a foot or so of bark, but the next winter got to 19F, and it didn't grow past a foot for 3 years until it finally died, which may have actually been from drought. After trying at least 200 seedlings or so thats the result. Although some will grow back 2-10 feet after a couple mild years, I expect them to eventually be stumped again and probably never produce. I keep them around for the idea to use as rootstock in the future. However, a grocery store seedling is not a tested clonal rootstock variety, so it 'could' be a gamble using them as rootstock in a given area in the first place..
The mexican types I haven't had cold issues with themselves, but since these grafted varieties available around here are grafted on less cold hardy rootstock, the graft union must be buried, which could 'potentially' cause future problems (I haven't run into major issues burying grafts so far, to my knowledge, although I have read not to do it). I think burying the graft with a good barrier of perlite around the immediate trunk/graft area would be best to discourage potential rot fungus and pests from attacking the underground graft. Then I would put a layer of clean sand on top, to hold heat down when it does freeze hard (since perlite can be pretty loose and might dissipate heat faster without a barrier). I would not bury the graft in contact with rich soil, out of caution. Also I tend to put some limestone at the very top of the sand close to the trunk and pour normal strength miracle grow solution right on the trunk base when fertilizing. It contains some copper and sulfur, which I believe is a bit of a fungus preventative whenever the trunk/graft gets briefly drenched, as well as obviously fertilizing, but I would not go overboard and fertilize too much and also not in the cold months.
You could also mound the less hardy base/graft with bags of mulch/leaves/pine straw during bad freezes and uncover it in the spring. A few cinder blocks stacked up circling the graft packed in with leaves, styrofoam or other insulating material might also work but i cant tell you to what degree. Or try a combination of these techniques. I leave out the prospect of using Christmas lights because its not really feasible if you wanted to plant a number of these.
We're fixing to get a 21F freeze in the next few days..I may put a few tricks together on some seedlings just to see what may work best.