Hmmm.. I really can't say anything for sure, but the 12 hour flowering cycle reminds me of cannabis.
I'm not sure how similar they are when it comes to flowering them, but I know that if it is like cannabis in some regards, you might not want to flower your original, but maybe a cutting.
With cannabis, after it's finished it's flowering process, it's natural action is to die. So hopefully that isn't the same case with the salvia. It's possible to re-veg cannabis but it's a very long, slow process and doesn't seem like it's very easy on the plant.
The best way is to keep a mother plant in 24 hour green cycles and put the cuttings into the 12/12 flowering cycle. That way you can keep your genetics for future crops.
Something else to consider is if you implement the 12 hour light cycle, I know with cannabis, that schedule has to be pretty strict with no interruptions to the dark cycle. Photo-shock can cause all types of weird issues.
So like I said, I really don't know if these issues are the same for sally and cannabis but if they are, you'd definitely want to be aware of it.