[Sexan]

Here I've added adding more buttons from F1 menu :

local defstr = table.concat(col_main, " ")..","..table.concat(col_hover, " ")..","..table.concat(col_bg, " ")..",".."0"..",".."a or m"
      
      -- added 4th and 5th options for adding menus (number of menus and menu type)
      local retval, retstr = reaper.GetUserInputs("Settings", 5, "Main RGBA (0 255):,Hover RGBA:,BG RGBA (requires a restart):,Add Menus,Menu Type,extrawidth=24", defstr)
      
      if retval then
        
        local col_arr = {string.match(retstr, "([^,]+),([^,]+),([^,]+),([^,]+),([^,]+)")}
        col_main = {string.match(col_arr[1], "(%d+)%s+(%d+)%s+(%d+)%s+(%d+)")}
        col_hover = {string.match(col_arr[2], "(%d+)%s+(%d+)%s+(%d+)%s+(%d+)")}
        col_bg = {string.match(col_arr[3], "(%d+)%s+(%d+)%s+(%d+)%s+(%d+)")}
        
        
        --- if number of menu is added (differrent than 0)
        if string.match(col_arr[4], "(%d+)") ~= "0" then
        
          -- save all entrys ( current open menu , number or menus to add, menu type (action or submen)
          new_buttons = {cur_depth, string.match(col_arr[4], "(%d+)"), string.match(col_arr[5],"(%a+)")}
          
            -- to how many buttons were entered
            for i = 1 , new_buttons[2] do
            
              -- if new menu is action
              if new_buttons[3] == "a" then
              
                -- set action to nil and label is set to "action" + last menu + 1
                newA = { act = "" , lbl = "Action "..(#mnu_arr[new_buttons[1]]+ 1) }
                
                -- add new button to existing table 
                mnu_arr[new_buttons[1]][#mnu_arr[new_buttons[1]]+1] = newA
                
              -- if new menu is menu/submenu
              elseif new_buttons[3] == "m" then
                -- allow creating submenus only in main menu
                if cur_depth == 0 then
              
                  -- new menu/submenu
                  newM = { act = "menu "..(#mnu_arr[new_buttons[1]]+2), lbl = "Menu "..(#mnu_arr[new_buttons[1]]+2) }
                
                  -- new action
                  newA = { act = "" , lbl = "Menu "..(#mnu_arr[new_buttons[1]]+2) }
                
                  -- add new menu entry at current menu
                  mnu_arr[new_buttons[1]][#mnu_arr[new_buttons[1]]+1] = newM
                
                  -- add one new action in that menu (so it is not empty)
                  mnu_arr[#mnu_arr+1] = { [0] = newA } 
                end 
                              
              end
              
            end
        end
        
      end

It can add actions or menus (menu type "a" for action "m" for menu), menus can be only created if we are in main menu, if in sub menu only actions can be created (it will discare if you enter menu type "m" nothing will happen)