I have a mirror and an object in front of it. I want to hide the reflection of that object and show instead a reflection in the mirror of another object hidden in that scene,is that possible?
I slapped together a quick example. In short - The visibility options for the first object (Suzanne) have glossy, shadow and diffuse turned off.
The second object (cone) has only visibility for glossy enabled.
This results in Suzanne not being visible in the reflection and the cone just being visible in the mirror.
Depending on what you're needing, there might be more involved ways of doing it via compositing, but I hope this answers your original question.