I tend to think that all that could be done would be to maximize the stains genetic ability to produce resin/THC. I dont think you can make a low resin low THC plant into a high resin high THC plant no matter what you do but taking the same genetics and growing them in optimal conditions for their genetic code will get the most out of them but no more.
That is only my opinion of course but I tend to believe it to be accurate.
Look at Durban Poison, it is an African strain from Ethiopia. Part of Ethiopia is equatorial and part is subtropical but even though it is a landrace strain that has grown there for like ever it still does not have a really high THC level. It is darn good pot but no breeder/seedbanks rates its THC level very high so if existing in an equatorial region getting more of the sun/light rays that the information was about actually means an increase in TCH over time, as in something of an evolutionary process, it doesnt seem to have been the case with Durban Poison. That is unless many years back in time it was extremely low in THC and has grown to what it is that is still far short of many other strains.
That is why I tend to believe that increasing certain light spectrums may maximize a plants genetic ability to produce resin/THC but that it cannot make it surpass it and reducing those light spectrums will decrease its production of resin/THC.