I've heard urban legend that you can poke a branch of a veging plant thru the light barrier and flower JUST that branch?
Have done it twice to prove a point , no effect moved beyond the stem in flower , behaves as two seperate plants.
When half a plants in full flower and the other half is in serious reveg am not quite sure what to feed it , and resort to foliar on the veg side.
Same if half is male , hormones controlling flowering dont seem to move beyond the branch in 12/12 or 24/0 , seeded of not.
As its very easy to do this in my stacked room with the flower above the veg , will run another this way and show some pics.
Its interesting to see what you can do with canna , but most of it is not very practical unless only very low numbers can be kept , and grafts can fail later for no apparent reason which is why i explored multiple mothers and eventually went back to standard.
If you search tomato root grafting , there is fresh interest and plastic products to simplify the process.