Hello Sherylbobbins,
I have removed fungus from my axolotl's gills while she was in the salt bath, so I'm pretty sure you'll be alright to remove the fungus from the legs especially because it covers such a large surface.
I don't know much about the pain receptors of an axolotl. Although, I am researching a book called "Copeia" at the moment so I might find something worthwhile. Some part of me also recalls watching a documentary on the use the axolotl's regenerative abilities and a scientist severing the tip of an axolotl's tail. Also, another member on this forum amputated part of their axolotl's tail as well.
Jay.