I am trying to make it so that the accounts can log in, but they keep showing an incorrect user/password. To prevent this, I wanted to try assigning a row in a spreadsheet to one thread. Is this possible?
Export your spreadsheet as csv file, than import it to BAS as a resource and set it to use each line 1 time (it is default setting I think). That way each thread would take new line from your csv file in run mode or as compiled bot.
The same way like you did it before, just load cookies and apply fingerprint, and eventually save as profile so your cookies and fingerprint would be saved for future use - next time you only need to load profile which will preserve fingerprint and cookies.