Suggestion: Left Alt as Extend about bigbagkbdtrixxkb HOT 2 OPEN

   lv5                  Key to choose 5th level
  lv5:lsgt_switch_lock Less/Greater chooses 5th level; acts as onetime lock when pressed together with another 5th level chooser
  lv5:ralt_switch_lock Right Alt chooses 5th level; acts as onetime lock when pressed together with another 5th level chooser
  lv5:lwin_switch_lock Left Win chooses 5th level; acts as onetime lock when pressed together with another 5th level chooser
  lv5:rwin_switch_lock Right Win chooses 5th level; acts as onetime lock when pressed together with another 5th level chooser
  lv5:caps_switch_lock Caps Lock chooses 5th level, locks when pressed together with another 5th-level-chooser
  lv5:lctl_switch_lock Left Ctrl chooses 5th level, locks when pressed together with another 5th-level-chooser

// The left (formerly right) Alt key (while pressed) chooses the fifth shift level.
partial modifier_keys
xkb_symbols "ralt_switch" {
  key <LALT> {
    type[Group1]="ONE_LEVEL",
    symbols[Group1] = [ ISO_Level5_Shift ]
  };
  include "level5(modifier_mapping)"
};