Chilli:
Thanks. Message received and I do bow to your professional knowledge. I was thinking this morning about what had been said on this thread. Although I was still uncertain, before flying today, I decided to change my SOP and switch to standby before changing code. The change was no big deal. This thread and your comments have now convinced me as to what may be better practice.
So, I'm sorted out, and thank to you and the other experts. As you say, many instructors are not giving clear advice on how to change squawk. Perhaps the Air Pilot should be more specific? Or would this be over the top?
I'm only a PPL, but it behoves me to fly to the highest standards possible, especially when IFR in CAS. What do the professionals do? I'm genuinely interested.
It seems this topic is a good example of PPrune's value.
Regards