I just stumbled over a script i made long ago..
Sometimes you have the problem that you made a hole only to find out that its to big than its a lot of work to redraw the object.
This script can help:

This hole is to big:


Select al faces of the hole and choose the basepoint (normaly the center ):


You get a cutting tool:


Change the diameter of the tool, perhaps stretch it:


And you have your smaller hole:


Have fun