Honestly, you’re pretty close.
Use code similar to what @jpark posted and add a column to your dataset to use as a flag. When you need to refresh the item which is being modified just set the proper flag in the dataset and your custom renderer will just take care of the rest.
All you need do is have the script check the flag column for each data point.
Note: This will allow multiple points to be formatted so if you only want 1 point to be changed you will need to insure that what ever method modifies the dataset does so correctly.