Are my ending options restricted depending on secondary objectives completed?

In the last level proper of DE:HR, you are given two secondary objectives which eventually match up with two of the possible choices at the end of the game.

If you do not complete these objectives, are you unable to make the corresponding choice at the ending?

If so, how are you restricted? Do the corresponding switches simply remain non-interactive?

You are correct. You will not be able to access the ending corresponding to any of the two secondary objectives left incomplete - at the time when you make your choice Eliza simply won't mention them and the buttons will be unavailable.

The other two endings are always available regardless of what happens.