To the discussion of validity of write-ins, peruse the below cited stipulation from RCW 29A.224.311, (3)c

The name proposed written in for position 6 already appears on the ballot, and the position the Mirror wants you to write-in is not PCO. Odds are great Elections would invalidate any write-in votes for a filed candidate cast in another position. 

The link provided from the Mirror would not address this special circumstance. 

A call to elections for clarity must include the fact that the proposed write-in for pos.6 already appears on the the ballot for position 4. 

If Elections was not clear about this, a general question about write-ins would not properly address the concerns raised here.

Calling on the nuance about 'filing for the write-in' VS getting votes written in, but risky at best.  I'd get it writing.

(3) No person may file as a write-in candidate where:
(c) The name of the person attempting to file already appears on the ballot as a candidate for another office,