Almost every GUI action results in the issuance of a Tcl command. The creation of an IP including the setting of all the customization options can be performed in a Tcl script without user interaction.
You would need to know the names of the configuration options, and the values to which they can be set. Typically, you first perform the customization through the GUI, and then create the script from that. Once you see the resulting Tcl script, you can easily modify the script for your needs, such as changing data sizes.
Tcl script based IP creation is useful for automation, for example working with version control system. For information about source management and revision control, see this link in the Vivado Design Suite User Guide: Design Flows Overview (UG892).