Chronos writes:
Not really, unless we consider that they’re being published under the byline “R. A. Heinlein” instead of “Robert A. Heinlein” constitutes use of a pseudonym.
Heinlein used “Lyle Monroe” for pre-WWII short stories that he didn’t think were up to the quality of his Heinlein/MacDonald work.
More information on Heinlein’s pseudonyms and other Heinleiniana can be found on the Robert A. Heinlein Home Page (and, before anyone asks, no, I am not James Gifford).
AFAIK, Murphy never used the Merriwell or Maxwell psuedo-psuedonyms prior to There and Back Again. They were created for the series.
From what I can understand from her afterward to Wild Angel, the third book will be metafiction about how you write differently whether you think of yourself as male or female. Neither Merriwell nor Maxwell are characters in the first two books, though “they” will probably be characters in it.
A more straightforward example of this sort of metafictional conceit was the book Lords of the Swastika by Adolph Hitler. 
Thanks for clearing that up, RealityChuck. (Was going to shorten your name to just ‘Chuck’ but then read the sentence aloud…eeeeee…)
Sounds tres interesting, will have to look those up.