Is it possible to check if a dlc is active in the current campaign?
And if a dlc is not active, is it possible to activate it during the campaign?
Is it possible to check if a dlc is active in the current campaign?
And if a dlc is not active, is it possible to activate it during the campaign?
No, DLCs cannot be activated if they were not enabled when the game was started.
As for how to check, it depends on what you mean.
For the added storylines (Slingshot and Progeny):
As for the Enemy Within DLC:
If you launch in vanilla, you can't load EW save files. If you launch in EW, you can't load vanilla save files.