Fare combinability: *A P fare + J fare (EOS question)
 

I'm looking at the very tempting DUB-HNL fares which allow travel on Jan 2, 2017. However, I'd like the return to be past end of schedule as published. Would it work to buy a full flex J return ticket and then downgrade that to a different P/Z fare when the desired date + fare comes becomes bookable?
(published fares expire on Feb 2 and I would not want to wait in case they disappear)

Anyone have experience? Thanks for insights!

2,300 views and no replies tells me nobody has risked 6k on a full J ticket to attempt this :) Thanks for the implicit feedback! ^