i would be very happy to get the seated pax working for the well known Prosim737 Aircraft (B737-800NG) Do i have to wait until its maybe supported or is it possible to change the Aircraft myself to get it working ?
There's no way for users to add Seated passengers support for any airplane, because we need to generate custom 3d files for each airplane that are added to GSX set of objects and are created by custom software that is written to integrate into the GSX build system.
In addition to that, the installer must recognize any airplane explicitly, and take into account all the various quirkiness and methods various developer use to setup the airplane and its add-on liveries folders so no, it's not accessible to users.
I don't know how that product works, other than knowing it's geared to home cockpit builders, so if it's true it has a modeled 3D cabin, it might be theoretically possible to support it, but I don't see how this could possibly be happening without some support from the developers, since spending €1500 for a "non commercial" license (and I don't see a TRIAL option) JUST to add passengers, doesn't make any sense for us, since normal cheaper MSFS add-ons are like 1000x more popular so, if you Prosim customers would bring up this matter to the developers, and convince them Seated Passengers are important to you, maybe they'll listen and would find some way to make this happen.