Can a mod be done to an expired task order to change the Ship To DoDAAC so that it will match up during invoicing in WAWF?
Good question; in a word "yes" you can issue this modification to your expired task order.
Although the terms "contract expiration" or "expired contract" show up often in the FAR, the FAR provides no formal definition of what that means. But when applied to a contract action it normally means the period of performance is complete and any opportunity for the government to have additional work done or purchase more supplies has passed (e.g. exercise an Option CLIN).
There is nothing in the FAR or DFARS that prohibits a contract modification prior to the contract file being officially closed. Often times modifications are needed after the contract is expired and physically completed in order to complete close out of the contract file.
The answer above assumes the basic indefinite delivery contract has not been officially closed, see FAR 8.404.