I started using the stick fast stabilizing liquid and have about a pint left. I would like to try cactus juice. Can I mix it with cactus juice so I don't have to waste the other material.

The resin you mention is a copycat of Cactus Juice and is the same basic chemistry.  Mixing the two will not be an issue assuming your other resin has not been contaminated by using it with oily wood.