worms

I have my soil mixed and cooked. I am reporting my veg plants into final 15 gallon pots in a rols soil mix. Could I add worms to this mix now or should I not add any at all?

I guess another question I have is should I add a small amount of nutrients top dressed during flower if I want to cut the plant at the stalk and insert another to put directly in veg or should I just add it at the end and let the soil cook for a month?

if they are redworms and you live in an area where the temps are ok, then you can absolutely add the worms to your soil, especially a 15 gal. your second question is a lil confusing, I think you're asking if you should amend the old soil for the new grow season WHILE the original plant is finishing? if that's your question, then NO, I wouldn't, you COULD, but i'd wait until after you pull the original plant before amending the soil.
if re-using soil, get very familiar with micro teas, aact, and mychorizae, hygrozyme (expensive, but growers like it for recycling soil,I don't use it, but I don't re-use my soil)
i'd start vermicomposting too
this site has some good stuff regarding vermicomposting, AND recycling soil