Hey there! That's a great question. While I have not sandblasted or frosted neon tubes, I have soldered stained glass to neon tubes before. I wrapped stained glass pieces with copper foil tape, and also put the tape on the parts of the neon where I wanted to attach the stained glass, then used flux and lead solder to attach them. I did this AFTER I processed the neon. More to your question, I would say just experiment and see what happens. If you sandblast the tube before you process it, I suppose it could crack on the pump as the sandblasting might create stress in the tube. I imagine my soldering onto the neon tube I made probably created some stress. This can be checked with a polariscope if you have one. (I don't have one but would love to get one). You could also try the sandblasting after you process the tube. Just make a little sample stick. The worst that would happen is it would crack the tube. You just gotta try it and see! If you do, I love to hear about your results. Here are a couple of pictures of my stained glass to neon tube.
