The source control operation used to store local changes on an instance for later application is called a stash.
A stash is a temporary storage area for uncommitted changes that are not ready to be pushed to a remote repository. Developers can use stashes to save their work in progress without committing it to the local repository or discarding it. Stashes can be applied later to restore the changes to the working directory, or dropped if they are no longer needed. References: [ServiceNow Docs - Stash local changes], [ServiceNow Docs - Source control]

"There are two possible ways to respond to events:
- Email Notification
- Script Action" - see this quote in link below:
https://developer.servicenow.com/dev.do#!/learn/learning-plans/tokyo/new_to_servicenow/app_store_learnv2_automatingapps_tokyo_responding_to_events

https://developer.servicenow.com/dev.do#!/learn/courses/tokyo
/app_store_learnv2_flowdesigner_tokyo_flow_designer
/app_store_learnv2_flowdesigner_tokyo_notifications_in_flow_designer
/app_store_learnv2_flowdesigner_tokyo_inbound_email_and_flows
"By default, the system generates a watermark label at the bottom of each notification email to allow matching incoming email to existing records." https://docs.servicenow.com/bundle/tokyo-servicenow-platform
/page/administer/notification/concept/c_WorkingWithWatermarks.html

https://docs.servicenow.com/bundle/tokyo-application-development/page/build/applications/task
/t_SelectAnAppFromTheAppPicker.html