They are normally pretty good in situations like this TBH.
Just explain your wife is struglling to get in & out of the car due to severe pain and an operation hasn’t helped, requiring her to need another one later in the year.
They may charge an admin fee for allowing you to change which can be upto £250 but, in cases like this its normally only small £50 or so, if any at all.
You will get a pro rata refund on the AP you paid for the CLA.