You can, to some extent, prevent users from editing your dialog. There is no absolute protection, though: expert users will easily edit your dialog anyhow.

• You can trap the menu event which toggles the dialog into edit mode. This is the Edit menu command. Insert in the script of the dialog the following handler:

  on do menu the_cmd to the_dialog
      if the_cmd is "Edit" then return
      continue do menu the_cmd to the_dialog
  end do menu

• You can delete the Edit ▸ Edit mode ⌘Y menu item. You would do so in the prepare handler of the script of the dialog:

  on prepare the_dialog
      set n to count menu item of menu "Edit"
      set visible of menu item (n-1) of menu "Edit" to false -- separator line
      set visible of menu item n of menu "Edit" to false -- "Edit mode"
      [...]

  This is reversible, a script can show the menu items back.

In both cases, the user can still toggle the dialog into edit mode by script:

set the_dialog to window 2
set mode of the_dialog to true -- into edit mode
set mode of the_dialog to false -- into normal mode

The user can also still edit the script of the dialog by script:

EditObjectScript(the_dialog)

You can prevent users from editing the script of your dialog. This is robust: the user may be able to break the dialog, not to view the source of your script. The mechanism consists in storing a separate script saved as run-only, and "manually" loading that script into the dialog.

1. Make your dialog normally.
2. Once your dialog final, save the dialog's script into two files: one that you will keep for future use, and one that you save as a run-only script.
3. By script, set the dialog's script to the run-only script:

   set the_script to load script (the_run_only_alias)
   set script of the_dialog to the_script
   save the_dialog in 0

The script of the dialog is now non-editable. To make it editable again you must first set it by script to some editable script:

set script of the_dialog to "property whatever:0"

then you can edit it again (but still you will not recover the run-only script's source, you must use your backup copy).