I'm with Vaun on this one, if you don't want staff changing the value, then don't make it an input box.
However if for whatever reason you have to have an input box and also don't want to let the agent change it,
You could look at the Disabled parameter under advanced, or Change Action also under the Advanced section which would let you run an Action whenever someone tries to change it and change it back or show an alert etc.

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Anton Vroon
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