Mass Import - Tasks

Thousands of Task records to be cleaned up by updating its Status to "Completed"

Unfortunately, we can't do it via Mass Import because of its current limitation, that is the inability to overwrite Task records via Mass Import.

(Tasks with associated SR's which is not yet "Closed", should be filtered out)

Does anyone know a workaround to be able to do this without settling with updaing the records one by one which is the worst solution.  

Many thanks!