Encontrei a solução sozinho: -)
$ xmodmap .Xmodmap
. O arquivo .Xmodmap
deve conter o seguinte:
'
! Swap Mod1 and Mod5
!
remove Mod1 = Alt_L Meta_L Alt_L Meta_L
remove Mod5 = ISO_Level3_Shift NoSymbol ISO_Level3_Shift
keysym Alt_L Meta_L Alt_L Meta_L = ISO_Level3_Shift NoSymbol ISO_Level3_Shift
keysym ISO_Level3_Shift NoSymbol ISO_Level3_Shift = Alt_L Meta_L Alt_L Meta_L
add Mod1 = Alt_L Meta_L
add Mod5 = ISO_Level3_Shift