Can a toilet on concrete slab be moved about 4 1/2 inches?
In the US, the typical toilet rough in size is 12", which I believe goes from the toilet bolts (center of the drain) to the studs (so subtract 1/2" for drywall). You can also find toilets made for 10" and 14" rough ins. But, to get more clearance, the easiest thing to do is swap out the style of toilet from an elongated bowl to a round bowl. If you're a man visiting the library, it means you have less space to hang free, but it gives you a lot more space to get around the bathroom.

To answer your first question, you can move the drain, but it involves taking a jackhammer to the concrete. Not a fun project if you don't like messes.