Redemptions always book into prime, rather than codeshare. And frankly Qatar does de-prioritise redemptions more openly than BA, in comparison to commercial bookings. So unfortunately you cannot rely on the -3 to +14 day rule on any Qatar operated service, that's a BA operator "perk". Moreover the usual Qatar stance is just to offer a downgrade or a move to another date of their convenience. Typically a redemption space is needed on the replacement service, though you can ask BAEC to check with the oneworld Liaison Desk to see if anything else can be done. Now if this is a through UK - DOH - somewhere location then EC261 will generally apply and EC261 does impose a wide rebooking requirement here, but getting Qatar to take that fully on board is easier said than done. Having said that, overwhelmingly trips do operate pretty much as booked, and so long as you recognise that QR's customer service has some limitations, that is probably as far as it goes.