You certainly can change the Xero or QuickBooks account that your A2X account is connected to!
The connection can be changed from within the connections settings page of A2X.
But first, there are some points to consider:
Accounts and Taxes Mapping
If you use the A2X default mapping then this will need to be reset so that A2X can re-create the accounts for you in the new accounting system's chart of accounts.
If you don't use the A2X default mapping then you will need to ensure the currently mapped accounts in your A2X mapping are set up in the new accounting systems chart of accounts.
Bank Account Mapping
If you are switching from QuickBooks Online to Xero you will notice there is no longer a requirement to map bank accounts within the connections settings page of A2X - this is because we post invoices/bills to Xero, not journals.
If you are switching from Xero to QuickBooks Online you will now need to map to the bank account/s you receive your Amazon deposits into in QuickBooks. This can be completed via the connections settings page within your A2X account.
If you are changing from one QuickBooks Online account to another QuickBooks Online account you will need to re-map the the bank accounts from within the connections settings page.
Cost of Goods Sold and Inventory Account Mapping
You will need to re-map the Cost of Goods sold and Inventory asset accounts from within the Cost of Goods sold settings page.
Marketplace Tracking or Classes
Marketplace tracking or classes need to match the old accounting system and need to be re-confirmed within A2X.
Refreshing of Settlement Data
Once all account settings are updated/changed it is important to remember to refresh the settlements in your A2X account - this will ensure that all current settings are applied to the settlements before you send settlements and cost of goods sold entries over to the new accounting system.