Coding replacement 5AS to existing ECU

Hi, Is the above an easy task please and where do I find the instructions. Thanks.

Is it possible to connect pscan to the original 5AS ?

The instructions are in the program in pscan - make sure you have all the remotes when you programme them as it clears the memory before adding them.

I can re-connect the old one if necessary.

Yes

Reconnect the old 5AS
Log into the old 5AS using pscan.
Use the "read EMS" feature in pscan and note the EMS.
Fit the replacement 5AS.
Log into the replacement using pscan.
Use the "write EMS" feature in pscan to set it to the value from the original one.
Once you have done this the engine ECU should recognise the replacement 5AS because it's sending the EMS code that the engine ECU expects.
You might have to turn off the ignition and lock the car for the new one to load.