what would be the impact of changing the account numbers for an inventory item?

It will update all the related records in the open period, if the transaction period is not open, you won’t be able to change the account numbers

hmm curious how reports will work, i guess old months will show old accounts and new ones new accounts

not sure, if it updates all related records in previous months, I am guessing everything will show you new accounts, because reports gets it data from the transactions