If the nut is loose you will be able to move the adjuster blade enough to get the chain off and cam out
Yes, but the adjuster blade and nut are stuck together, meaning that when i turn the nut, the "adjuster blade" turns with it.
If you can turn the stud, you can relieve the tension from tensioner shoe against chain. You'll need the chain slack to withdraw the cam.
Possible options: Use a nut splitter to crack the nut in half to remove it from the adjuster stud.
Insert wedges between head and nut to get it moving away from the cylinder block. (possibly with a large end nipper)
Cut the stud off along with the jam nut. Use a long screwdriver/pry bar to reach in and relieve pressure from shoe on chain. Shouldn't be too hard to overcome the spring tension.
You should be ready to replace the tensioner, you know.
Cheers,