Updating cost center to journal automatically using post transaction notification

One of my client has a requirement to update the cost centers that were tagged in marketing document but not in journal entries; as accounts were not set as expenditure or revenue, automatically. We are thinking of using post transaction notification for the same.

So, I wanted to know your opinion whether this is the only option or is there any other option to automatically update the cost centers that are tagged in marketing document but not in journal without setting the account as expenditure or revenue?

Also, I heard that if we use Post transaction notification for the same, then it will be taken as data tampering by SAP and will stop SAP support in future for that database. Is that true?