I never understood the multi-character troubles until now. Things need account wide.

[dinnertime]

You can also play pretend you have the mount/title/whatever even if you don't have it for that matter.

Or you can just go do the content with the character and earn it legitimately.

Or you know, pretend to not care if someone else wants their achievements on their alts especially when it'll affect practically nothing gamebreaking. Sounds like a reach to involve something like that with RP anyway.