I'll have to change the wheel bearings on my bike and I'm not sure about the thread on the locking ring. Is it right hand or left hand? I don't want to use a hammer and center punch to loosen them, as the four holes on both of them look a bit abused already. Looks like some kind of peg tool could do the job. Are there any other obstacles to watch out for?
As Kostas mentions, a suitable tool is not to difficult to make.
4 evenly spaced 3,0 mm diameter pins on a circle with a radius of 17,5 mm gives the tool to do it.
I made a 20 mm hole in the middle to push a large bolt through. The bolt can be used to press the pins of the tool into the nut. Not required on new rings but as you say they are usually damaged by hammer and punch.