Is their a way to make checkbox behave like a radio button?
Yes, but Why? If you want it to behave as a radio button, why not make it a radio button?
This auto-enter calculation would enforce a situation where only the most recently selected value is stored in the field--which is typical radio button behavior:
GetValue ( Self ; ValueCount ( Self ) )
and clear the "do not replace existing values..." option.
Retrieving data ...