Would it be possible to add more alcohol and repeat the process from beginning?
I wouldn't. Allow me to attempt to explain...(I am really medicated off NL hash)
The idea behind iso hash is to leach the alcohol soluble THC glands from the veg material. The only problem is that THC isn't the only thing that gets stripped from the plant material. Chlorophyll, and god knows what else is dissolved in the alcohol because alcohol is such a good solvent. So the longer its in alcohol, the lower the quality of the end product.
When I made iso hash, I would use scissors to chop up the sugar leaf and popcorn. Not finely like a joint, coarse, big chunks. Also, I would only use fresh, frozen material. Dry stuff breaks up too finely and too easily, IMO. I would put this in a mason jar, packing it in tightly. Then I would fill the rest of the jar with 99% iso, also from the freezer. Top the jar and shake it for 5 seconds, add a little more iso, shake for 30 more seconds and strain through a fine mesh, 140 + into a large, shallow glass baking dish. Allow to dry, alcohol evaporates at 76 degree F (if memory serves) and should quickly evaporate within a few days providing your house is warm enough.
CK