Here is a very simple modification for your Anet A6 printer. With these two parts you can adjust the height of the Z-Endstop. This is particularly useful if you want to print on a glass, mirror or any other surface other than on the provided tape.
The screw holder piece must be fixed with a M3 screw on the left Z carriage, just like in the picture. In order to do that, you'll need to drill a hole on the piece. Just lift the x axis as much as you can, remove the left flap where the rods are holded and you'll be able to drill the hole comfortably, without dismantling the whole printer.
If you feel uneasy about drilling the plexiglas frame, you can first do a mock up with double-sided tape to see the positioning of the pieces.
Another M3 nut will go on the Hex-shaped insert. Ideally this nut is self-locking and has already been threaded once. You don't want to do too much torque when adjusting the height. I used two little drops of epoxy glue (I don't like cyanoacrylates on PLA) to hold the nut on place. If you use a normal nut, the movement can cause wobbling and wobbling can cause the screw no move up and down.
De-attach the Z-Endstop from its place and put the offset piece instead. You'll be able to screw in the Z-Endstop a little bit to the right. Enough to match the screw on the carriage.