Right, I'm not sure what your point is. You can always add more fields, so being unable to change the type of a field isn't a problem, since you can introduce a

Right, I'm not sure what your point is. You can always add more fields, so being unable to change the type of a field isn't a problem, since you can introduce a new field and start using it. You cannot however, stop using a required field. The best you can do is set it to a nonsense value and leave a comment saying "well we need to set this to something, but we don't actually use it anywhere. Because to be sure of that you can remove it, you need to be sure that every storage system and every piece of middleware and every since thing that links your proto anywhere in the world that you might care about is upgraded, otherwise if they encounter a new message they'll crash. If you only have a single client and server, and you control both, this is doable. If you don't have that though, you cannot.