“Your house and electrical wiring is yours, and you have the right to do with it what you want. That said, we highly recommend you leave it to professionals.”

This is not mixed messaging, this is just advice. Mixed messaging would be something along the lines of: “Your house and electrical wiring is yours, and you have the right to do with it what you want. That said, you are not allowed to do what you want.” Mixed messaging colloquially means contradictory statements.

Likely not, the whole point of hydraulics is that the fluid is non-compressible!