How do I change texture of one object(plane) by clicking another

How can I change one object’s texture to one of many, each controlled by a different object?

I want to make this eventually:

A row of planes, each one’s texture changed to one of 121 textures, each corresponding to a different smaller image button (plane with click behavior).

So I guess the most basic questions would be:

  1. how do I change an object’s texture by clicking a plane
  2. how can I do this to the same target object by selecting different plane buttons