Sorry for being lazy, but if people could confirm or deny my understanding I'd be grateful.

Thinking of using avios and amex companion vouchers to book 4 Business Class seats to LAX. BUT may well need to cancel or change. Partly booking to avoid losing the option of the reward flight, as we are limited on dates. Am I correct in thinking that it's not an issue? If I cancel or change it would just be a £35 per person fee? Furthermore, could currently avoid the fee by taking a future travel voucher?

Also, am I correct in thinking I can ring BA and add a return flight, possibly even open jaw, at a later date, as long as such reward seats are available?

Thanks for any help.