On a modern Aircraft like the A320 or B737, is it possible to disable computer interference with the control inputs of the pilots?
For A320 it is possible also in the real aircraft. The problem with disabling flight control computers is that it also disables associated control surfaces. If you disable all five computers, you disable all surfaces and the aircraft goes in to "Mechanical backup" mode, which leaves pilot only the control of the trimmable horizontal stabilizer (ie. pitch trim) and rudder. Wide bodies are similar, although they have more redundant flight control computer architecture.

The correct procedure to override normal law in Airbuses is to switch two ADRs off, which forces controls to alternate law. This disables most of the protections leaving only load factor protection. All control surfaces would still be operating with automatic pitch trim. This would be used only in undue protection activation.