Hi,
These are separate commands when controlling via IP. To do what you're suggesting would require some black magic to make the command change when video playback is detected. Certainly not impossible, but I'm concerned if I make this change lots of other users will complain as it no longer functions the same as the native XBMC iOS app.
The user/password stuff is something i'm looking into. I've had a few requests to support different user profiles which requires this as well.
Cheers,
Matt.