Can/should you adjust the gravity after fermentation?

[Christoff]

Do you have a refractometer? If not, you should. And use it during the mash to monitor the progress. In fact, use it for all gravity checks up to the minute you pitch.
Do you use the Spike Solo for all your brews?
I would invest in some kind of fermentation temp control... And, what do you ferment in?

I just bought a refractometer, but haven't used it yet. So far I have only used my hydrometer.

I don't use the Spike solo for all my brews. Only when I want a bigger batch of something, or experiment with smaller batches of the same wort. I have a spike conical that I use to ferment those bigger batches, and I have the temp control package for it.

all the other batches I use wide mouth plastic fermenters or 1 gallon glass carboys. I have a small beer room that I can control fermentation temps fairly well. I just have to watch it a bit closer than the spike temp jacket.