That documentation tells how to allow users to see templates, but it doesn't really show how to hide them.
To hide them from a group of users, you need to put the Templates they *shouldn't* see into a category and connect that category to a user group (e.g., Administrator), that the users don't belong to with an Element Category Access ACL entry.
IOW, put all the templates on the site into a category (call it AllTemplates). Then update the Administrator user group. On the Element Category Access tab, create a new entry with these values:
Context: mgr
Category: AllTemplates
Minimum Role: admin Super User
Access Policy: Element
That will hide all templates from the Editors. In theory, that should hide them in the drop-down. Check to see.
Use the steps at rtfm to give the Editors rights to just the Templates they should have access to.
Note that the Editors won't be able to edit resources that use Templates they can't see. If that's a problem, see the note at rtfm.
You shouldn't have to use Form Customization.
More info here:
http://bobsguides.com/hiding-elements-in-the-manager.html
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PLEASE, PLEASE specify the version of MODX you are using.
MODX info for everyone:
http://bobsguides.com/modx.html