Seems like maybe there were a couple tweaks loaded into the system yesterday (it always seems to be Saturday morning when I discover any changes). My SFO-EWR flight in late May got pushed an hour back, so I called in to see what luck I would have on adjusting my entire PDX-EWR leg. First time I called in, I tried to change to PDX-DEN-EWR leaving earlier, but agent said no to that (which I think made sense - would have been a ~3.5hr change of departure earlier). Then I asked about simply moving to the PDX-SFO departure leaving an hour later, and I was also told no. The agent then said that her supervisor told her that 'schedule changes happen every 8-9 weeks anyways' and, in effect, why even bother now? Aside from being false (I see schedule changes more frequently), it seemed rather dismissive to tell me why bother...I would rather lock in the flights that I want now and change, if needed, further down the line.
HUACA, got an agent who pushed me to the later PDX-SFO flight with no questions asked - very pleasant guy. I decided not to try my luck on PDX-DEN-EWR but may give it another go if/when I get another schedule change that pushes the SFO departure (currently @ 3 PM) even further back (as I feel like the scheduling for p.s. flights becomes a bit sparser on holiday weekends).