Comment 5 for bug 171856

You should just be able to paste into the /share/extensions directory. I don't know what's going on there. I have two "Add Nodes..." entries in my "Modify Path" submenu, using those exact files. The second one for me is the new one. You did restart Inkscape, right?

if that isn't it, it look like the .inx file is incorrect, as Inkscape won't show it in the menu if that is wrong. I was going to reupload, but they are identical, and the uploaded copy works on my machine, so it cant be that. Same goes for the .py file.