I do have an answer for this, but I'm working today and tomorrow to get some projects done before CES. I'll try to write up a usuable explanation when my projects are done.

The short answer is that while you can't actually make a button "exist" or "not exist" with a variable, you can use variable and aliases to make a button that switches among various functions, then you can show or hide a separate button image with a variable. The end result in the remote is what you want: It looks and works like the button is completely changing appearance and function based on the state of the variables. that the button in that position appears to change in both appearance and function based on the settings of the variables.

Dale Crawford
Instructional Media Designer
Universal Remote Control, Inc.