Swap left Alt with left Win and use left Alt as 3rd level chooser

Swap left Alt with left Win and use left Alt as 3rd level chooser

how can i do such things mentioned in the title. If I use both the
swapping does not take effect but my alt key is 3rd level chooser and win
key opens the run prompt (?). Don#t know how it is called. I've tried
xmodmap to change the keys but without success.
I'm using German (Macintosh) as keyboard layout.
Thanks for any help.