If the parking spot already have a Quick Edit pushback, you'll see an additional option in the GSX menu:
- QuickEdit
- Use autosaved QuickEdit Pushback
"Quick Edit" will enter again in the Quick edit editor, allowing you to make changes
"Use autosaved QuickEdit Pushback" will just do the pushback as it was saved the last time, skipping the editor step
Also, if you select "customize airport positions", and choose the parking spot you have added a Quick Edit pushback ( you'll see coordinates there ), you can click "Customize" to edit, or the Trashcan icon to remove it.