Thanks for writing.
Yes, you can specify a custom text box template by setting your own DataTemplate object to the TextBoxTemplate property of RadConversationView. There is one special requirement and it is that you need to set the x:Name attribute of your custom text box inside the template to PART_TextBox. Also your custom text box must inherit from the system TextBox control. Fortunately RadAutoCompleteBox inherits from TextBox so you will able to use it.
Please write again if you have other questions.
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