Any good resources to learn rules for calling GTS to book Air France flights on Delta stock? It is referenced here: https://www.flyertalk.com/forum/35107674-post5.html

Specifically, I’m wondering the following:

• Assuming I know the Air France booking/fare code, is it priced same as AF.us directly?
• If schedule changes, does DL have ability to fix up like any other ticket?
• Assuming appropriate fare rules, if I cancel (or price goes down), can I get DL credit? (That’s ultimately the reason I am asking for)

Specifically, I am looking for CDG-Spain which DL doesn’t sell as a codeshare or offer on web (unless booked as part of a connecting TATL), and AF has the only nonstop route for on any airline. It’s for a trip later in year, I’m which I am flying to CDG a few days before on a DL ticket.

Right now I have an AF Fully flexed book for flexibility, but there’s a decent extra cost to do that. If I could cancel that and instead rebook on DL stock on a (non-BE) non-refundable but have ability to get credit back if cancelled, I could save a few $100 dollars each person, and worse case end up with DL credits, which I know I’d use.