1. No universal remote will have buttons which all have exactly the labels you would like. So the remote probably won't a button labeled 30sec adv. But with a UEI remote, you can easily assign the correct function number to some button. For example you could assign the function 30sec adv to the button labeled PIP Ch+.

2. DirectTV remotes are made by UEI, but they do not respond to the 994 command that is used to assign functions to button. So it won't work.

3. Yes, you will be able to control everything that the original remote could do, and perhaps have a few extra functions, if the combo unit is programmed at the factory to respond to the IR signals.