My "primary" site is English.SE: that's what's listed as the "parent user" of http://chat.stackexchange.com/users/5926/msh210, for example. Is there a way to change that, so my account on a different SE is primary?
On my profile I can see a [change] link right next to
A text box will pop asking you to type the site you want to put. Auto-completion is on.
Is that what your looking for?