Hey guys - couldn't see an answer to this, though apologies if it has been discussed!

I'm looking to redeem some Avios for a long haul flight with BA next summer, the outward journey is now available (but has limited seats remaining) but the return (a month later) is not bookable yet. To add complication I want to use a BA AMEX Companion Voucher on the booking.

Am I right in thinking I could secure the outward leg by booking a return now (with a random return date that is bookable) and then subsequently change the date of my return flight at no cost...? Have people tried/done this? Does it work?

I could book the journeys separately but then would only have limited use of the Companion Voucher... if it goes horribly wrong can you cancel completely for a small fee right? Do you get the tax/fuel surcharge back?

Thanks!
Jerry