I sort of disagree. The best way to make people not rely on a behavior is to not have that behavior. If you want to be very, very sure that nobody relies on you

I sort of disagree. The best way to make people not rely on a behavior is to not have that behavior. If you want to be very, very sure that nobody relies on your service having very high availability, forcibly reduce its availability. Make sure it fails some small percentage of the time. Similarly here, if you need to make sure nobody's depending on this thing, change its name regularly. Append a random number to the end of it and change it with each minor release or something. Now, what you do NOT want to do is randomly pull the plug on your service or change the internals exactly once, with no notice, after a long time of stability. That's not helping people know not to rely on it; that's just hurting people who didn't read the sign. Quietly putting up a "deprecated" sign without ensuring people have time or opportunity to read it, waiting an unreasonably short time, and then breaking things is basically a Douglas Adams storyline more than a development practice.