I tested it, and it works! Thank you Jean!

PS : all these actions are still pretty bad (for example when they ask for ID you won't have to use what is called "ID" on steam, but the "name"). I used hundreds of different Playmaker actions on this game, and the steamworks were the only bad one (broken / incomplete).
It will be enough for me to finish my current project though, so I'm happy, but if someone really want to make a lot of things with steamworks, using Playmaker only, it wont' be possible (in the current state of these actions).