hi,
yes, that's possible, and it's actually not really related to photon.
If you are pulling the avatatr image from an online system, then the gameObject that is instantiated using photon, will know the user id it represent, and then it can broadcast a message ( a regular playmaker message, not a rpc event), so that the gui responsible to shwo the avatar know which user is now present.
if your avatar images are simply stored in the assets, then it's basically the same process, but it doesn't get the texture from an online source, but simply from a fsm var that you have filled up, either hardcoded ( one fsm var for each avatar) or using arraMaker to host a more flexible list of avatars you can poll from.
Does that make sense?
basically, this has nothing to do with photon in a way. try to do it first without any photon related feature, simply instantiate a prefab and tell that prefab that it needs to show its avatar to the gui. If you can do that, moving into a photon based prefab will simply be a matter of rerouting that call.
bye,
Jean