To use a comma after a user name (such as Q.E.D.) should I replace the final period or leave it?
Q.E.D,
or
Q.E.D.,
Peace,
mangeorge
I don’t think there is any situation in which you would replace a period in an acronym with a comma, whether the acronym is a user name or not.
Unless you want to infer that Q.E.D. is missing his period. 
Most style manuals I’ve seen state that you should place the comma following the final period of the abbreviation: “Q.E.D., are you crazy?!”
But, if the abbreviation is at the end of a sentence, a second period should not be added: “You’re crazy, Q.E.D.”
I’m not really crazy. Really.
Cool. I changed it several times, but finally left it the other way. I like this way better.