What I'd like to know is if the tabulator had the capability to subtract votes from the total count in the machine?

For instance, if a poll worker mistakenly ran an invalid ballot through a tabulator and then noticed their mistake, could they press a button and run that same ballot back through the machine and it would subtract the selections on that ballot from the tally?

If this is possible it would explain how a poll worker could easily remove Trump votes in the middle of the night. They could do this with a stack of calibration ballots in the polling place (that only have a vote for Trump) that are used to validate that the machines are counting properly.