I would prefer for my posts to appear as 'by nickname' than 'by owner'.

Found how to do this

Users -> select profile ->
Identity
Identity shown (drop down with several options)
:)

Hi barberj. Welcome to the forums, and thanks for posting your solution. :)

The bit you found is for the footer area where, if your skin has it, you see "copyright 2009 by {{name}}". But also obviously you found how to tweak what gets displayed in the posts :D

By the way you're right about if you want to change stuff in a skin you would have to edit the skin's files. Like add or remove a locale flag or not show the author name or stuff like that.