I suppose that your form is bound to the table that it is saving to, so once you make a change, it automatically updates that table. I'm not sure exactly how you have it set up, but you could have each option button to change it's value by creating an even on the AfterUpdate section by writing this:
YourOptionBox.Value = ABS(YourOptionBox.Value)
this will take whatever the value is, and make it positive. Let me know if this helps, or if you're saving to an unbound source.
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