I can suggest you, to disable the RadAutoCompleteBox, since you want to prevent the end user to add, edit or delete entries. You could use the Enabled property set to False.
Please note that with the usage of the aforementioned property, the appearance of the control would be slightly changed. If you want to persist the standard rendering, I can suggest you to use the property and remove the applied css class (racDisabled) with jquery in the following manner :
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