Have tried website chat. Got immediately referred to refund link but on further questioning relating to Flight number change was effectively advised I've only 2 options:

1) accept the schedule change via link within schedule change notification email (ie new Flight number)
2) change +/- 1 day.

I've got multiple flights booked from from 21st September onwards.

Apologies i must correct myself. I was originally booked on FR1456 departure at 19:40 on 21/09. That appears to be cancelled so they've moved me to FR1452 departure at 15:45.. However I just noticed there is a FR1456 scheduled to depart at 18:55 on 22/09. I conclude the FR1456 is not operating every day hence my confusion. !!

I guess it's back to the webchat tomorrow!

As ever with Ryanair one learns something new every time!