I did this last year when I bought cheap Ryanair tickets to Estonia and rebooked them after the flights got canceled. It works. Note that rebooking two-way tickets on the website is tricky if only the outbound flight has been canceled - the automated rebooking process won't let you change the destination, you have to go through the chat (which takes time). Rebooking one-way tickets was very simple - a link for rebooking appeared next to the canceled flight, it had the usual Ryanair rebooking interface except that the price of rebooked flights was shown as zero.

Not doing it this time - because due to Covid-19 restrictions, I doubt I will want to fly anywhere this June.