This thought started off as 'If we are in a simulation, or if there exist a God/omnipotent being that can change the laws of physics (and everything) as we know it - is it possible for a change to defy reality as we know it?"
The most dramatic example I could think of is 1+1=3.
Ex: One shoe, another shoe, bam - 3 shoes.
Theoretically, if we were in a simulation, the laws of logic could not be changed. A simulation must run using the rules of the universe it is contained within, and thus the “real” universe would have the same rules of logic as ours.
If we’re discussing what an omnipotent being could do, it depends on what you mean by “omnipotent”. If this Being is the Judeo-Islamic God, then yes. God created the idea of existing concepts and non-existing concepts, as well as whatever’s in between. This includes logic itself, despite how fundamental it is.
If we’re talking about some sort of magical wizard who can manipulate the universe however he wants, then no, he can't manipulate logic. [See below for the reason.]
Is it possible for us to be completely sure that 1+1=2 and there's no other way around it? Or, am I having a trouble conceptualizing this simply because I've lived my whole life in a world where 1+1=2 and laws of the universe are possibly more fluid than I had originally imagined?
Logic isn’t some arbitrary set of rules, like physics. Logic dictates that if there is a loaf of bread, and also another loaf of bread, then the only things in that group are those loaves of bread. This is what 1+1=2 means on the simplest, most fundamental level. For 1+1 to equal three, there has to INHERENTLY have ALREADY been a third piece of bread, despite me adding ONLY one piece of bread to another.
This would apply even in thought: If I would mentally picture my house and your house, I'd be picturing three houses, not two. These three houses would consist of your house, my house, and... that's it. However, this number would be three houses. In the theoretical universe, this would be normal and totally understandable.
This would even be true if nobody’s picturing anything: If there is a tree in Alabama, and also a tree in America, then in the 1+1=3 universe, there are three trees in all. Nobody has to be thinking about those trees, and they don’t have to be close to each other; just by existing, that conceptual group has to consist of three trees, not by magic, but because it's the only reasonable conclusion.
One more example: A sandwich has to have two slices of bread to be considered a sandwich, but in the 1+1=3 universe, the first slice and the second slice together would equal three pieces of bread. In that world, this would be completely logical, conceivable, and non-contradictory, just like the number of bread slices in OUR world's sandwiches.
So no, you're not just "used to" 1+1 being 2. There is no more fluidity in logic than the amount of cabbages in the color blue.
(Note: Although I am indeed curious if 1+1=3 is possible in a theoretical world, please note that this is just an example for a bigger question)
The most powerful theoretical wizard couldn’t make any of that happen, nor could any extra-universe alien who’s simulating our world, or any being to whom any logic applies in any measure. Only the Judeo-Islamic God could change logic itself.