I have an Avios booking for ABZ-LHR-ATH next year and want to make changes to this (bring outbound forward by 24hrs and shift return back 24hrs). I can't do it online, and normally would call to sort this out, but understandably can't get through. Can I just cancel online and use the FTV/e-vouchers for the tax portion of the rebooking?

Frustrating to have to cough up the Avios redeposit fee, but since the phone lines are swamped it seems like this is the only way forward. Thoughts?