[LEV = Longevity Escape Velocity, the idea that research will be able to extend lives faster than existing people are aging].  

If it's expensive and rare, nothing will change.  If it's cheap and common, everything will change, and what happens to criminals who have no appeal chances is one of the least important aspects of it.

My genuine best guess is "they don't, actually, get offered longevity extension; prisoners can't even expect to get life-saving prescribed medicine or obviously indicated treatments (eg to get a broken leg splinted), let alone HRT or anything elective; also, approximately no one has incentive to let prisoners get (presumably expensive) longevity extension therapy, unless it's to make damn sure they serve every last one of those 30,000 years."

The meaning of "life sentence" appears to vary wildly from one jurisdiction to another. Anywhere that specifies a duration, people would probably just serve out their time. Elsewhere, some new law would have to get written in light of the new human lifespan.