On the Prusa MK4, nozzles can be cold swapped.

The procedure is actually far easier, faster and likely safer than removing the heat block as originally documented.

After having cleaned your nozzle as documented (heat at 250 degrees for 5 minutes + use a brass brush), wait for the nozzle to cool down, manually unscrew the two big screws on the left, hold the heat block, and unscrew the nozzle to replace it.

This wrench perfectly fits the nozzle head and makes unscrewing the nozzle a breeze. 

A metal part is not required. The wrench is very robust and is not going to break.

Simple and quick to print. PLA is a perfect choice, as it's stiffer than PETG. Use 3 or 4 perimeters. Infill is not important. Print flat as in the file to maximize the strength.

Great video showing the tool in action, by Jiu Reviews:

Video