What are you talking about? 1 plant is 1 plant, 2 plants in the same container just means less root room and many potential problems. I really do not understand what you are trying to accomplish here...
If you think that you can plant 2 plants and have them genetically merge into one by their roots intertwining, then no this is impossible. Genetics can not be passed through roots. Genetics are passed by pollination. Just like humans, plants have DNA, it is kind of like a white guy, can never naturally turn black, no matter how long he hangs around black guys, it is genetically impossible. It is also genetically impossible for Nothern lights to have any genetic influence on a Haze plant that was planted in the same pot.
What you will influence is the root zone, with 1 of the plants becoming the dominate plant. Your plants will fight each other for nutes, water and light. They will both very quickly become root bound, and it will be almost impossible to seperate the roots in order to transplant them.
Basically you if you plant 2 plants in one container all you will do is stress the plants probably to the point of death. Just remember that roots have 1 major function, that is to let the plant feed, they are basically little wicks that pull the liquid and nutes into the plants digestive system, kind of like our mouths.
Also THC is good for me...It is a fact that you can take a clone from a still growing branch by cutting away the outer bark applying some rooting hormone and then covering it with some damp paper towel and suran wrap. The area where you cut will actually produce roots while still attached to the host plant. This helps with cloning hard to clone strains or for emergency cloning late into flowering. But doing what you said kind of falls inline with what i just said, you can not genetically modify a plant that easy, it has to be done on a cellular level by modifing the plants original DNA.