John,
I'm a little confused by your question. I've worked access before, and you can script updates in VB without issue.
In SQL, you should be able to alter existing rows in a table with a statement similar to

"UPDATE table SET field='foo' WHERE keyfield='value"
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are you specifically saying that this doesn't work with (I assume) DBD::ADO or DBD::ODBC? If that's the case, what statement in your script is generating errors, or what's preventing from executing such a command?