Shoutbox

You could do this to an extent with a quicktext. Go to Plus!>Preferences>Message helpers

You can then create the following quicktexts...
/nick <name #1>         name this quicktext /1
/nick <name#2>          name this quicktext /2
so on and so forth.

Your name would not change automatically but by just typing /1 or /2 or /3 etc you can easily change your name