i've never done it, but you can definitely graft a clone into a root stock of a freshly cut mature plant. It actually will create a hybrid phenotype as there is plant stem cell exchange that occurs. You can do this of any related plant species, the more closely related the easier it is. I've heard of/seen pictures of weed grafted onto hops roots before, but never in real life so idk. You can also graft two clones together by twisting to seedlings together so when they grow the stems will rub against each other, and eventually just growing together. This happens in nature as well.