I'm an avid player of Achaea, the Iron Realms flagship MUD, and I feel everyday that the choices I make with my character affect the lives of other characters, with some work and willingness change can and is effected, whether from assisting with city development to rebuild locations, or from plotting, conniving and overthrowing a government, it is possible!
In Achaea, at the attainment of experience level 99, you are gifted with the ability to take on the form of a dragon, you choose your colour, have a public ceremony if you wish and unless you lose level 99, you can transform into a dragon at yuor whim.
The greater dragons in Achaean lore played a huge role, and it is this soul that the worthy player is given. There is a small range of colour choices for the new dragon and the descriptions for each are static. Very occasionally an auction will run whereby someone can bid and win the right to a customisation of their dragon looks, but it is a rare thing.
I'm an advocate of this sort of control in this instance. While the majority of a roleplaying population are reasonable and intelligent folks, you will always get the one or two who very much want to be the fur-covered, purple, psychic, mini-dragon with fairy wings. This sort of alteration flies directly in the face of the established canon, and so regulation is used to enforce the roleplaying standards of the realm.
With this sort of regulation in mind we also have the opportunity to design and craft foodstuffs, clothing and jewellery. Again though the designs and ideas are submitted for approval to what is known as the Crafter's Guild, and only if a proposal passes canonical and grammatical muster will it be granted to be made.
I approve of and enjoy the immersion that this sort of regulation brings to my favourite, free to play MUD. Perhaps if you are looking to play a new game, or considering creating a game of your own, these considerations will give you something to think about too.