Yes, you're exactly on the right track! So long as you are only considering diatonic modes that is. All diatonic modes have 7 notes in them, and there is a mathematical limit to how many ways you can organize 7 notes within the western tuning system (welcome back to mathematical combinations, pick one, choose one sound at all familiar?). There is one mode name for each possible arrangement of modal whole and half steps, so if you invert the series you will naturally get one of the other possible arrangements.
In answer to the second question, you can get a Locrian sound out of a Lydian piece, but it may temporarily shift the aurally understood pitch center. If you wanted to incorporate a Locrian scale in a Lydian piece, all you would need to do would be to start on the 5th note of the scale and ascend up the Lydian scale. (starting on the 5th note of the scale and ascending according to Lydian will give you H W W H W W W). So it will sound like a "So" based Locrian. For example, if you are in C Lydian, your scale is C, D, E, F#, G, A, B, C. If you start on G and go up, you will still be using your original C Lydian mode, but the order of whole and half steps will make it sound like G Locrian. Hope that helps!