First of all, usage changes over time. In case you’re not familiar with the concept of time, here’s a link. For example, it used to be fine to call black people “colored”, as in the National Association for the Advancement of Colored People, but if you called a black kid a “colored boy”, people would look at you askance. Do you think the Washington Coloreds would work?
Second, how people in the in-group refer to themselves doesn’t necessarily change whether or not it’s a slur when used by others. For example, black people often refer to themselves and their friends as “niggers” and gay people may refer to themselves and their friends as “faggots” or “fags”. Do you think the Washington Niggers or Washington Fags would be acceptable?