Just to be sure I understand the issue :
you have a radio button that determines the content of another field, and you need to have the other field update correctly.
The mechanism to accomplish that is quite simple once you know it. The first step is to make your radio button field refresh the document when it changes (in Field Properties, 2nd tab, click on "Refresh fields on keyword change" option).
Once you have that, updating your other field will depend on whether or not that field is a keyword field or not. If it is, you need to make it update its choices on document refresh (same tab as before in the Properties), and design a formula that selects the options correctly.
If the other field is just another field, you need to create a Translation formula that does the job.
Pascal.
I've got nothing to hide, and I'd very much like to keep that away from prying eyes.