How can _system_selected_document_number be updated after an action is run?

**This post was created as part of a How to Service Request (SR)

Release: 22A.2

Summary of the question:How can we implement functionality where an advanced modify action will run logic based on line items that have been selected using the OOTB checkbox (_system_selected_document_number). Afterwards all the selected lines should be automatically unselected. The current issue is that _system_selected_document_number cannot be modified by BML as the following error is returned when attempting to specify a blank value in a bml function: Variable name _system_selected_document_number cannot be found.

Supporting Documents if any: