I am thinking of writing something in present tense. I started on something, but came across a problem. The story is in 1st present tense. Am I allowed to shift narration and do something like, ...unknown to him, exc. Changing a narration perspective, or no? This is a fiction.
Not sure how you would shift unless you alternate chapters or something? I write first person present tense, the trouble I would envisage is you need to have a clear voice for each character. Also character interaction is different for example: I have Socrates who is the lover of Nate. Socrates sees Nate differently to the way Socrates' younger brother Angus would Nate. If I use Nate's POV then I need to get to know Socrates and Angus very differently again. OR The Abbot is Angus' headmaster, he is Socrates' friend and boss. Socrates and Angus intereact in a very different manner with him. If you can do it and not making it confusing you have my admiration, only way I ever achieved it was splitting the book in two and having one character do one half and one character the other half. It was in a sense two books.
You could try starting a new chapter from another characters pov and see how you get on. 'Trial and error' play around with it.
Changing from first to third person is pretty jarring, because it's like someone telling you about a personal experience and then saying "and now, a word from our sponsor" followed by an ad for Kleenex or something. If you want something to happen "off stage", change it so that it's first person past tense told in the present tense. So:
If you want to change perspectives during the story, third person will probably work better. I usually only write in first person if I have a specific reason for wanting to do so.
What do you mean, "am I allowed"? Are you worried the literature police will kick down your door, beat you up and revoke your poetic license? You are allowed to do whatever works. Write it and see whether it works or not. You can always change it when you go back and edit it -- you were planning to do that. weren't you?
Yes, you can do it. You can shift POV, tense, etc. as you see fit. It is your story, and as digitig notes, there are no literary police in force at this time. But you run the risk of doing it poorly and detracting from the work (jarring the reader or whatever). So unless you have a good reason to approach it in this fashion, or are absolutely confident you can pull it off, it might be better to take a more traditional approach.
