Hello Louise Lecourt (LouiseLecourt),

Yes you can add the Status for an entry even in Studio:

You need to have a termbase opened in your project settings, then you select the term in the source part and in the target part and with right click you chose :"Quick Add New Term"

Then please make sure you are in "Flags Layout"

Then you need to click the Edit button and chose status and preferred and the save button

Hello Louise Lecourt 

You can simply open the termbase viewer hover over Status and then select Approved/Forbidden/or indeed Preferred

Is this what you are looking for?

You can also edit your termbase definition in Multiterm to add the fields you need. Go to Termbase Management, select Definition, right click and select Edit.