Sorry I missed your original question ? Yeah as UPD says try it on something first. Is it clear or a colour ? It should be okay so long as it didn't actually freeze ? If the tin has started to rust it might taint the colour slightly but essentially as long as you keep it warm now and make sure you shake it for at least 2 or 3 minutes before you use it you should be okay. If in any doubt though get a new one.
Platikote works fine, don't get it on the windows though. I usually unmask the windows and then remask them, makes it easier to get off once you've put the solvent based paint on.
Make sure your shell is absolutely dry though and put the first 2 coats on real gentle otherwise you'll get a pickle
