You can't save the template directly, but you can use this workaround:

• Select the template you want to change from the dropdown list.
• Make the changes you want in the template.
• Select "New template" from the dropdown list, and enter "Temp" as its name.
• Save the changes as "Temp"
• Select the original template from the dropdown and click on the trashcan symbol to delete it. Confirm the deletion.
• Select "Temp" from the dropdown list.
• Select "New template" from the dropdown list and enter the original template name.
• Save the changes.
• Select "Temp" from the dropdown list.
• Click on the the trashcan symbol to delete it. Confirm the deletion.

After this procedure you have the changes saved not quite in the "original" template, but in one of the same name, so the final result is the same.

Thank you!