I believe the cbd trait can be lock in just as any other trait can be. It would take testing obviously however if you did you initial f1 crosses and the grew out those seeds selecting only those with the cbd trait m/f (again test verified)and crossed those again getting f2s find the cbd trait again and hit that with known cbd pollen which you saved from the previous generation would begin to lock it down. From those bx seeds you again select from tested cbd chemovars continuing to save known cbd pollen. I definitely think the cbd trait could be locked it to say 4 different phenotypic expressions say thc/cbd 1/1, 2/1,1/2,1/4. All it would require is space, the ability to test, the time/desire to do the work.Or you take autoflowering hemp like finola and mix it with an autoflower that has high thc.
Yes its true that finola generally doesent have very high cbd. However there are phenotypes of it that do give extremely high cbd. Breed that into picture more with finolas if you want to make sure of high %. You dont have to, but cbd levels wont be as consistent.
Amount of cbd OR thc is co trolled by same gene, its the expression of that gene that determine whether its high thc, high cbd, but those gene expression types can mix and make up 1;1 thc cbd strains.
When you first mic high thc with high cbd(and no thc obviously), you get 1/4th high thc, half 1:1 and 1:4th high cbd.
Its not impossible stabilize those further, stabilizing af with af-photo is much harder.
Now if you think that there is no way to make sure of the thc/cbd levels of the parents for new seeds because you cant clone, you are wrong. If you keep track of what pollinated what plants and then test those plants after they died and made seeds, you can select to use only the seeds from good parents. Yes using photos and clones makes this easier, but its definitely not impossible or too hard for people who breed these strains for living. Just a bit extra work.
Also you can clone cannabis just from some plant tissue, you dont need cuttings. From what i know of autoflowers, i dont believe in some knternal clock to trigger flowering. They start to flower when they are ready for it, so i think in theory cloning from leafs should work just like with photos or tomatoes.
Thats my opinion but I could be way off.