You can now use the upgrade planner tool to have your bots automatically upgrade all lightning rods on an island to lightning collectors.

(The upgrade planner is the green button on your toolbar. If you have never used it, you should try it out. It is extremely useful. Also try putting it into your inventory or hotbar, and then right-click to customize it.)

To make the lightning rods/collectors replaceable, I made them both 1x1. But since the lightning collector's sprite is bigger, I had to scale it down. So now it's smaller and shorter than the lightning rod, which looks a bit weird. See picture.

The mod can be added to an existing save. Any lightning collectors you've already built will have their positions off-grid, but it doesn't cause any problems. (There is one exception: if you try to downgrade an off-grid lightning collector into a rod, robots will try and then fail to place the rod off-grid, so the downgrade will get cancelled. But upgrading always works.)