>>15250858>>15250871Pokegen is both a save editor and a Pokémon editor. When most people mention Pokegen, they're referring to the latter, which can be done independently from save editing; in fact, more people probably use Pokégen together with GTS spoofs than they do with save files, since those require either an emulator or external hardware.
Unless the first guy meant ROM instead save; not being able to access the ROM will certainly slow down the creation of a PKX generator, but it won't prevent it by any means. It's still entirely possible to acquire that data through trial and error.
You could download one of the sample PKX files they link to, open that fucker up in a hex editor and set its dex number to 719, send it back to your game and see what happens. Rinse and repeat until you run out of Pokémon. Then do the same thing with the moves, held item, ability, met locations, etc. Once you run out, you go back the other way until everything gets back to zero.
Congratulations, you now have all the data to code a 6th gen PKX generator. The ability to extract and reinsert PKX files is the first step. All that remains is the datamining (well, someone else will have to figure out how they did this first, since I'm sure they're not eager to tell other people how to send their hackmons back to the game).