when I find Nodal point on my camera, and I zoom in, is it necessary to rearrange camera?
Yes, the nodal point changes. If it does not, its purely coincidence!
Each time you change focal-length, you will need to recompute the nodal point of your lens. Note that this is also true of focus on most lenses but the difference is not very pronounced and should only be noticeable when focusing at close (macro) distances.
It does yes, because the iris diaphragm moves as you zoom (usually).
This depends on what camera/lens you have.
If the nodal point is important for your shoot, then yes you may need to rearrange.