These things can only be done with scripts, not expressions. I'll move this to Scripts Discussions.
To add an expression to a property you would use:
property.expression = "my expression";
To remove an expression you would use:
property.expression = "";
To convert an expression to keyframes you would have to loop through the time of each frame in the comp, storing the times and the values in arrays, before removing the expression and setting property.valuesAtTimes(theTimes, theValues).
To separate dimensions, I would consult the CS4 scripting changes at:http://blogs.adobe.com/toddkopriva/2008 ... ng-ch.html
And of course, feel free to ask more questions if you get stuck.