The only problem here is to get the related CI attributes. update the event is fully documented in the examples (HPBSM\opr\examples\epi-scripts)
From a quick look at the API (/opr/api/doc/opr-external-api-javadoc.zip), it looks like you can get the related CI Id and related CI type, but not the attribute.
one option here is to use the UCMDB API from the groovy script, and get the CI properties by its ID and Type. this will work, but may cause performance issues if you will go to the UCMDB for each event.