Disappointing as this answer may be, but you cannot. You can change the xkb options that are available, but you cannot do other things which are not exposed through the xkb options.

That can be done with xmodmap, but unfortunately, that tool is not always reliable in modern desktop environments. It may stop working after you put your computer to sleep, or if you attached a different keyboard or switched to a different keyboard layout (e.g. different language).

So it cannot be done with xkb options, and using xmodmap has its issues. The only way this can be changed is by customizing a keyboard layout.