Can't change classic rewards flight

Hi All,

On the 16/4/25 I booked SIN-HEL-LHR for 1/4/26
and then booked a return LIS-HEL-SIN for 5/5/26
There availability for LIS-HEL-BKK which I wish to change to for the return however since my ticket was booked so far in advance the ticket validity is exactly 1 year (until 16/4/26) so I can no longer change flights that happen after this day.

Is this normal, how does anyone even book a RTW fare if they can't add more legs or change after the first ticket issue with availability of business seats so scarce they need to be booked a year in advance.