In Episode 69 the Sages of High Wycombe very briefly discussed the diplomacy required when playing a character in a game set in a world that one has created. Professor Cule seemed a little startled to discover that Professor Bell_West has done that. I’ve done it at least eight times that I recall.
Two of the long-term players in my SF setting Flat Black, veterans of the first campaign and several others, each ran something in it twice. One tried two campaigns of Secret Service intrigue involving setting-busting developments; I played Lord Tacitus Arbeiter in the first (which was unsuccessful) and Lt-Major Miles Scrivener in the second (which worked okay). The other ran two one-off adventures of straightforward criminal investigation in which I played characters whose names I don’t remember. Those were both fine, though my character in the second was killed because of a representation problem in HERO System.
Three different friends have run campaigns or adventures in my fantasy setting Gehennum, one of who was one of the Flat Black GMs and also an original and long-serving veteran of the setting. I played Bluefin, Methlin, Albion, Ivrian of House Green and Scarlet, and Ivrian Immanides “Evander”. The campaign with Bluefin in it was okay, I think. The others were all unsuccessful for various reasons.
If I’ve distilled anything useful out of these events it is that if you are in a party where you know the setting better than the other players things become especially difficult if you play the person in charge. It’s better in that case to play a very capable expert in specialist role.