$ xprop -root _XKB_RULES_NAMES _XKB_RULES_NAMES(STRING) = "evdev", "pc104", "us", "altgr-intl", ""
I can see that this property on the root window contains five strings. But I found no way with
xprop to set it! The tricky part is to set a string array so that it looks like shown above.
xprop can’t do it another tool is fine, too.