You can change it if you are playing on a co-op game or your own server by modifying the BlocksConfig.ecf file. The file needs to be changed on the host machine.

By default, the file is located in:
Steam\steamapps\workshop\content\383120\2550354956\Content\Configuration

Make a backup copy of the BlocksConfig.ecf file before you make any changes.
Open the file in a text editor. (I recommend Notepad++, its free and is much better than notepad)

Search for: Block Id: 684, Name: TurretGVDrill

Look below to find this line: AllowPlacingAt: GV, display: true

Change it to: AllowPlacingAt: "SS,GV" display: true
(Make sure to include double quotes " " around "SS,GV" !)

Keep in mind that any modified files in this folder will be overwritten anytime the scenario updates, so you will need to repeat the process when that happens. Unless you make a local copy of the scenario, but that would also involve starting a new game - this method should work ok for what you want to do.