Can someone tell me which function behind the point "After using a command hyperlink, deactivate it"? For me this does not seem to have any effect.

there's many ways of doing this, as there's different designs of it:

if they're Verbs (items in the built-in 'displayverbs' and/or 'inventoryverbs' Stringlist Attributes on/within Objects, using 'list add' and 'list remove' Functions):

http://textadventures.co.uk/forum/samples/topic/5023/how-to-use-display-verbs-and-inventory-verbs-effectively
http://docs.textadventures.co.uk/quest/guides/using_lists.html
http://docs.textadventures.co.uk/quest/using_lists.html

http://docs.textadventures.co.uk/quest/scripts/list_add.html
http://docs.textadventures.co.uk/quest/scripts/list_remove.html

Dictionary Attributes too:

http://docs.textadventures.co.uk/quest/using_dictionaries.html

you can mess with the UI/pane/JS customization stuff, removing/hiding the input command bar, and etc stuff (Richard can help you with this stuff)

you can find the built-in 'Command' handling coding... and adjust it as wanted

you may be able to manipulate the Command's 'pattern' String Attribute:

// say you get silenced (can't cast spells)
// set (combat_command, "pattern", "attack;defend;item;escape") // this is not how to actually do this type of stuff... just a concept example

<command name="combat_command">
  <attr name="pattern" type="string">attack;defend;cast;item;escape</attr> // this is not how to actually do this type of stuff... just a concept example
  <attr name="script" type="script">
    // scripting
  </attr>
</command>

etc etc etc

Where can I find this point in Quest?

It makes the text processor commands' hyperlinks disappear.

msg ("You can {command:look}.")

Default:

With the option checked: