I was told by my grandmother that when the children went to school it was just a simplier way to spell the name.
My Bernard McMenamy actually is shown on the records for Oct. 9, 1848 as follows:
Barney McManomey and Margaret Currens
Now that was a new spelling but don't forget the information was being give perhaps with heavy brogues what have you. I have them in 1880 as McMenamy and that is what is on the ship manifest I believe. Correct spelling was not that important perhaps since so manyn people could not read let alone spell. I remember when I lived in Pittsburgh meeting some "green horns" right off the boat by a year or so and sometimes you could not understand a word they said. :)
So I don't have your McMenamy information right at hand I packed it all away several years ago. Possibly we could match something up when I can find more information in Ireland if possible.
I have a friend interested at work in geneology and she was adopted so it is interesting. The one lead we thought we may have had was in Chicago has not responded since she found out that my friend was left in a basket on a church step.
Talk to you later.