Ha, yeah, good luck. You can get a GUESS at what will happen by using a tool like ExpertFlyer to see what fare class the fare would book into if it booked onto a SA-marketed flight, but that will not tell you what the LH codeshare fare class translates into.

Best you are gonna do is buy (or hold) the ticket then look at the SA view of the reservation and check the fare classes they see then cancel it if it doesn't work for you.

Even for carriers who don't offer a free 24-hr refund, you can usually get an ARC void from a travel agent, for example Orbitz is pretty good about cancelling trips within 24 hrs of purchase for almost all carriers for free (which is a thing that travel agents can generally do). Worst case, if LH doesn't offer 24 hr free refund on the itinerary you want, you can usually book with Orbitz then check the SA view of the itinerary to see what the fare class is and cancel/refund.

After you do this exercise, please report the fare class you get — it is proprietary/secret knowledge and publishing it publicly will help educate consumers.