Yes it's tied to the key, but Honda did not start putting them in their cars until 2001. You are missing the details in my message.
And YES, OBD is tied to emissions and diagnostic standards. NOT immobilizers. Yes you can swap the ECU to a different year model as long as you have the harness to convert to fit that OBD(X) hardness.
They changed diagnostic standards when emissions regulations changed. Thus OBD0, OBD1, OBD2A, OBD2B/CANBUS standards. PLEASE research it more before quoting people as being incorrect.
Also I had to look back at Preludes as they did have immobilizers on the 97-01 models. This was not an issue for Civics or Integras until 2001.