It would be better to leave everything connected. Less chance of things to go wrong or for mistakes to creep in.

Coils and coil harness comes off first, then switch and lamp harness. Coil harness will be largely separated from everything else, switch and lamp harnesses will be more intertwined.

And just to reiterate - the heavier coils (e.g. flippers) can come off since those are expected to be replaced every so often. This helps reduce some of the weight and strain as you move things around. (Plus yo can then hang it out without things getting too twisted). The wire harness itself will “remember” where everything goes, it’s pretty amazing

Use masking or better blue painters tape to mark key lights / coils, and place a loop of tape over the harness where the wire retainers are in the game. This will assist in lining things up later on

I’ve only done a few playfield swaps, however I’ve have found that using *Ideal wire markers* can be a life saver. They are particularly handy if I want to do a major teardown of a major mechanism on a bench.

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Take lots of pictures. When you think you have taken enough, take even more.

As has been said, remove the heavier coils. I remove all the coils, leave the switches and lamps connected to the harness and throw the whole thing in the dishwasher. This gets rid of the years of dirt and grime. You may end up crushing a few switch blades, but they are cheap and easy to replace as needed. Let it dry for a couple days while you do all the other work.

Pictures..did we mention for your sanity..lots of pictures! Best wishes with your swap.
-Mike