That depends what you mean, as in like they can edit the logo from their UCP? if so you'd need to add in a mod to phpBB, which currently in Beta 5 is not supported and you will NOT get technical support if you have it in a live environment...
Another thing if you do make the mod they will release RC1 and then you'd have to re-write the mod... so why make the mod just to re-write it later hmmmm?
But yes to answer your question you'd need to create/install a module (aka mod).
If you really want this then try looking around some sites with phpBB 3 in a live environment... i.e. http://www.startrekguide.com/