Access write conflicts with views and insteadof triggers?
Access uses the values of all columns to decide if a row has been updated by some other process between Access reading the row and subsequently writing to that row.

You can prevent that behavior by adding a TIMESTAMP column to the table(s) in question.  Access will then use the single TIMESTAMP value to determine if the row has been modified by someone else.

The only way to prevent that error message is to not update the row prior to Access attempting its own update.  I would make Access modify the two fields currently being modified by the trigger.