My app supports landscape left and right orientations. However, once the up is initialized and the initial orientation selected, I'd like the orientation to lock and not change anymore.

Fore example if the user started the up with landscape left, it will stay landscape left for the runtime duration of the app.

Is there an easy way to do this?

Apple insists that a user be able to use a landscape app in either landscape orientation; if you try to force it your app may be rejected.

Thanks. So is there a way to let the user lock orientation with a software switch?

Well, if a user wants to lock their orientation they can actually do that themselves either using the switch on the side of their device or an option in their dock. (It depends on their settings.)