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.
Select "Mix Lines" in the resource, that way all the lines are mixed and thus it will have a random line. Or you can use javascript to mix the array list using function shuffle to get a better constant randomization. I believe there's also the option "Shuffle List" under the "List" option