Adjustment to previous year's expenses

Hello! I do the bookkeeping for 2 condo buildings that used to operate as one - one bank account, one set of financials, etc. Since 2017, they operate as 2 separate entities with their own accounts with expenses being split 50/50. I was just informed that common expenses have to be split 54/46 and not 50/50. I'm not sure how to  make adjusting entries to the affected categories for each year so I can refund the money to the building that overpaid and charge the building that underpaid.  I'm assuming I can't create a journal entry for each affected category because it will change the financials from previous years. So do I add some type of "adjusting account" and just bundle the refund and the over payments in there so the categories remain intact? Do I bundle all the adjustments from the previous years into this 1 account? It seems very overwhelming and I don't want to make a mistake.  Thank you!