You may use any valid WDW ticket at Disneyland. You take your ticket to the gate (not the ticket booth) and the CM will take your ticket, take a day off of it and give you a Disneyland ticket for the day. If your WDW ticket is a parkhopper, you will get a parkhopper, if your WDW ticket is one park per day, you will get a one park ticket.
It's very easy, but you can only exchange the ticket for the current day's ticket - that is, you can't trade in your extra 5 days on your WDW ticket for a 5 day parkhopper.
Have a great trip!
Yes. I thought you were including my clarification in the word valid but since the wording in the OP said "at a later date" I thought the extra clarification might help. Of course, with the OP having over a thousand posts they probably didn't need it but someone else reading it might. I'm always overcautious.
Walt Disney World Resort Annual Passes are not valid at the Disneyland Resort in California. Likewise, Disneyland Resort Annual Passports are not valid at the Walt Disney World Resort.
Also, not necessarily every valid Walt Disney World Resort ticket is valid for admission to the Disneyland Resort. In particular, select non-expiring tickets issued prior to the implementation of the Magic Your Way Ticket Program in 2005 may not be used for admission. The only way to know for sure is to present said tickets at any Disneyland Resort Turnstyle.
Walt Disney World Resort Annual Passes are not valid at the Disneyland Resort in California. Likewise, Disneyland Resort Annual Passports are not valid at the Walt Disney World Resort.