Grafting can be used to change certain properties of plants. Basically anthing that is controlled by chemicals in the sap is altered by grafting. So pest resistance, disease resistance, maybe drought resistance if the cultivar has naturally weak roots. You can use it to produce certain types of fruit in ecosystems that it wasn't bred for. But the physical parts usually stay the same. The fruits look, taste, smell the same. The leaves stay the same shape. If it is healthier on the graft than it is on it's own rootstock it may have larger foliage and fruit with stronger branches, but if it's golden delicious it will still be golden delicious and will not turn red or have granny smith tartness even if it is on one of those rootstocks.

The problem with grafting is that it does not help the plants genetics. It is popular for fruit trees because breeding programs take FOREVER, you have to wait anywhere from three to five years to find out what you got with a tree variety, so there are several lines which are not continuously improved simply because grafting is very economical for something which will produce a crop year after year for 25-30 years. You have about a year when the graft is very vulnerable and you have to keep on top of your pest and disease control.

I believe it could be done successfully with cannabis but you can run breeding programs through two to three generations per year easily, so the time is better spent improving your variety.

I am only an armchair expert, so if anyone with more experience in the orchard business sees something wrong or wants to clarify something I've said I'd like to hear it, and I think the OP would too. Grafting may be useful to give you a target to aim for so to speak. You find a good grafting combination you know there's a chance to develop a strain like that by breeding the stock and scion together possibly? And a graft may heal up a lot quicker with a high metabolism plant like cannabis than on a fruit tree. I don't know, but I'd like to try sometime. Maybe that's my next experiment!!