I already was able to change the icon of the Main Menu in the panel of Mate using these suggestions
Yesterday, suddenly menu was gone, I fixed it and eanted to assign "my" icon again, doing the same procedure. This time it did not work...
I started dconf-editor
mate > panel > menubar add my requested file name without and with or without path: Mein Menu icon does not change (that is the one with the little arrow on top). I use the Numix Circle Icon set, and want to have an icon from the very same set. Do not understand, because i did it once, and it worked
To the suggestion below saying: "if you want to have a custom icon, copy the .svg image to /usr/share/icons/apps/image.svg replace image with the image title of course..."
I do not have such a path... /usr/share/icons/apps... Thanks for any help