Is it okay to thaw frozen brisket and re-freeze?

Cut a big chunk off while frozen. Boom.

I am the smartest man in the world.

Fill your sink or something deep enough with cold water. Put the side of the brisket you want thawed in the water up to the point where you'd like to cut. If you can't cut it with anything while frozen, you should be able to do so in short order when it the side you want to cut softens a bit. Vac seal the side that remained frozen and put it back into the freezer.

I bought some frozen large pork chops from a farm and they came frozen in a vac pack of 4. I only needed 2, so I put the pack in the sink so that the two were in the water. They softened up very quickly, so I could pull them apart from the other two chops. Vac sealed the other two and put them back in the freezer. Worked great. Using the other two this evening.