I found this page after some searching: https://quickbooks.intuit.com/learn-support/en-ca/employees-payroll/recent-updates-to-td1-basic-pers...
Seems like the message is that there's no need to redo anything as it's not a large enough amount to be material, and your employees will get the overpaid amount back when they file their tax return. I'm just going to adjust manually going forward and set a reminder for myself to doublecheck the amounts for Jan 2021 in case the 2021 compliance update doesn't override the manual amounts I entered.
