They use the specific language replace/extend/exchange for award tickets. Maybe my time spent in the BA forum is making me a bit pendantic, but it leaves me with the impression that these may be different from other changes. If not, they'd just say "any changes", and then they'd link to their fees. On the other hand, it doesn't specifically say partner awards...so maybe I'm just paranoid

Maybe it would be better to ask people here if they've had to pay any "unexpected" fees when they've made changes to partner travel?