Not necessarily so. He could go with a single phase double set trigger that does not require a fly, but as I said earlier, it may require some additional wood removal, and a bigger trigger guard. That is why I suggested a single set trigger.In order for a lock to function properly with double set triggers, the lock must have a fly in the tumbler to lift the sear over the half cock notch.
To answer you question, no it is not simple, especially for one who does not totally understand the mechanical relationship between lock and trigger/triggers. No disrespect intended. There are many variables that need to be considered once the overall inside mechanics are determined. Different locks, and triggers fit like mixing Chevy and Ford parts.I mentioned in another thread that I like my Dart brand full stock .45 cal rifle but would swap out the single trigger for double set triggers. I have never removed the trigger from the rifle for a look but I wonder, is it usually a simple conversion/swap.