"boosters" don't change genetics. those products that promise 'bigger buds' are just lying. A "booster" is probably just heavy P/K. One of the most common ingredients used will be monopotassium phosphate. This isn't special or unique. it's used in all sorts of fertilizers not labeled 'booster' or 'bloom'. it's just fertilizer and like all other fertilizers should be applied at correct concentrations... more is not better.. more leads to toxicities.
You can say "plants need pk in flower" but if the application causes a toxicity, clearly too much was added... toxicities don't 'boost' anything excepts worse results.
Properly feeding them is all you can do. Excess feed results in toxicities. It's not foie gras. There's no product that caues big buds beyond simply providing a healthy rate of all nutrition the plant needs. Finding an upper threshold and backing off of it is probably better than erring on light side, but regardless bombing it with excess is a gauranteed bad idea.
Your plants look healthy enough with very minimal symptoms seen. the yellow leaves at bottom could just be the plant shedding them... if it continues to creep/progress up the plant you will need to adjust fertilizer formula to increase N provided. Fertilization is a culmination of what you have provided more so than what you did last week, i.e. adding some 'boosters' for a week probably doesn't do shit for the plant.
They could have made use of more light, though. Growing outside? So, not necessarily within your power to do so.
Genetics dictates potential cola size. An over-crowded canopy (not the case here) can cause smaller buds / same yield per sq ft. Feeding it properly can allow it to meet its potential. You can control some aspects and impact results a bit, but only relative to geentics. Only certain plants are capable of growing donkey dick colas.
You've got a happy plant well more than halfway through flower phase... you could treat it like absolutely shit and it'd still turn out okay. Keep it happy.. you are doing fine.
*** stop thinking in terms of advertised flower time. It's 7 weeks.. not 7 of 9. it may take 10 or 12... the breeders tell you a best-case scenario that sells the most seeds. They measure from the taint with no shame, lol. 10" with a 6" taint. You simply observe and react or else you allow nonsense to impact when you harvest. Once the plant looks fully plump, start scoping trichomes... simple as that.. remove all other things from your head in regard to when to harvest. The plant in front of you is reality.