Rebiasing necessary for Lonestar power tube replacement?

Is rebiasing necessary if I want to replace my power tubes?

If so, how would I do this?

Your LS is fixed bias. As long as you buy tubes that are within 'Mesa spec' then it will sound great. Tubes outside the range of the spec will not sound good is all. You'll have either too much break up or not enough and both will make your amp sound terrible. If you go with Groove Tubes then just make sure the tubes have a distortion rating between 4 and 6. If you go with any other brand be sure to buy online at a reputable store (thetubestore.com, tubedepot.com, dougstubes.com, eurotubes.com to name a few) and tell them that the tubes are for a Mesa and must be within spec and they'll send you the right pair.

If you have a LSC then I have some JJ 6L6s with very low hours on them if interested. I also have a brand new 5Y3 rectifier tube in case you have a LSS and want to replace that tube.