If you want to update your content without sending out a new Serial Number, then just load the new content and save the project. Only send the new created database (.AIPFILE file - see file names) to the user. If you installed an update of All-In-One Protector, then you also have to deliver the new All-In-One Player.
Sending out a new license file would destroy the product activation information and the user would have to activate the product again.
If the new content should be usable only with a new Serial Number, then copy the project, using the option: New project uses a different encryption. This duplicates the complete project but uses a new encryption with new Serial Numbers.
If you use the installation manager, the field OverwriteLicenseFile controls, if the license file is overwritten or not.
The best option is to send the file via download link to the customer.