I'd say that it depends on the computer. Bluray readers are not directly connected to the video output on a computer. The bluray acts as a storage device, storing an encoded video. Since the stored, encoded video will not change, the computer is likely to decode the video to the same pixels each time you play a bluray.
So you would expect the output to be the exact same every single time you do so. But depending on the current workload the computer has to deal with, it may or may not keep up with de decoding process. The video output might experience stuttering or screentearing. Sometimes ever artifacts when a GPU has been overclocked too much or some hardware is failing.
Some video's are encoded with an algorithm that makes it possible to define a decode 'quality'. This means the software will choose a quality based on usersettings and the amount of work the CPU or GPU can handle.
HDMI often supports an audio output, and audio is very likely to put through some equalizing and possibly some other filters. This is done with all kinds of algorithms.
Even though you might expect the exact same binary signal, it could appear otherwise. I think it's very unlikely to measure the same signal twice, but I'm not saying it's impossible..