Hi,
I cannot see the whole code block, but if the workflow is still registering the error as mentioned by you and the only concern is to avoid the 2nd table update. Then why don't you put the 2nd table update under the IF condition if you do not want to use the RAISE exception.
As workflows are event triggered thus a RAISE is required as the its not like a normal report or code.
Cheers,
Arindam