Import additional data to existing records

Hi, I am wondering if it is possible to add (some) data to existing records using one ID field as cross reference.
For example I have a spreadsheet, one column 'ID', and a handful of other columns with the corresponding field names. I want to import those to exisiting records where the ID value is equal to a specified ID field in the existing table.
The new value should overwrite any existing data.
The default import function seems to import only new records. Could the above be achieved with a script? Could anyone put me in the right direction.
Thanks