I think you’ve got a bit of a problem there. The whole point of the radio code thing is to make theft less attractive to the oiks who do that sort of thing. On the Mk.3, the code isn’t accessible to the user, it’s stored in the ECU so that the unit can only be used in the original car (if you reset the unit it picks up the code automatically, you don’t have to - or can’t - enter it yourself). With a replacement unit I guess you’d have to either reprogram the ECU or change the code in the new unit to match the one in your car. I know that’s possible because my car’s head unit was replaced under warranty early on, but in your case you’d have to convince Honda that the new unit wasn’t stolen.