I got a lot of locks for a new hotel (bungalows), and I want to make one side of the locks inaccessible to any key. (They have 3 doors so only one needs a key for both sides). Is there some way to make the exterior lock hole to not work but allow people to unlock from inside?
You can use a "Killer Key" to permanently block the key slot. Either buy one or cut your own as shown below. Once you insert the key, the deep square cut catches on the pins and it can not be removed. Snap off the key at the weakened point and you're done.
If I understand your question, you're looking for a single sided deadbolt. It has a knob to lock or unlock on one side and nothing on the other. Here's a link to an example. Many others can be found by searching for "single sided deadbolt" or "one sided deadbolt".