Once you have printed the allotted number of copies and confirmed that they printed successfully, you cannot print a piece of music again. Each printed copy of an ePrint sheet music purchase is a purchased copy, just like a traditional copy printed by the publisher. If for some reason you lost a traditional copy, you would need to purchase it again to replace it. The same is true for ePrint.
You can always access your ePrint purchases through your online account and/or by using the ePrintGo app.