Fly AA J all the way

Can one add cities to an award reservation on hold as long as it's within the requirements of that particular award class? Here's the scenario: some family members wanted help finding F awards ORD-LHR-CDG. I found the two Z seats they needed, but they were the last two.

I put them on hold right away. My thought was that, worst case scenario, they spend $500 for two BA tickets LHR-CDG. It's an overnight connection at LHR, so no worries about missing the flight and not being protected. However, they'd prefer (for obvious reasons) to just have CDG included in the award. They aren't willing, though, to risk losing the F seats they already have.