Well, that was a lot easier than I expected!
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My CoreXY heated bed has always been a pain: it had the 120W-ish RepRap Mk3 aluminium-plate heater that took anything up to 30 minutes to get to 100C (even with a cover over the surface), lost a lot of its heat when the hot-end was close to the bed due to cool air spilling from the hot-end's cooling fan, and so on. So I replaced it with a Keenovo 200W silicone-encased heater stuck onto a new piece of aluminium tooling plate, and then anticipated a tedious job aligning everything up and re-tuning the heater (remember that previously for each pass I had to wait for it to cool to room temperature (20 minutes or so) then 20 - 30 minutes to re-heat, with a fair chance of a tuning error on the way due to the extended delay).
I was wrong! First, I guesstimated the levelling by eye, then used the G29 command to see how well I'd done. Used the map image to work out where the bed was high or low and adjusted the screws accordingly. It took 3 passes to get almost all of the image coloured green - about 5 minutes elapsed time from start to finish.
Then I tuned the heated bed following the Wiki instructions - about 6 minutes to get to 110C without a cover, then it took about 30 minutes to complete all 3 phases of tuning (the new tooling plate has a LOT of thermal mass so the last phase took a long time).
So, due to Duet and David's software, fitting the new bed heater has proved to be a totally painless task - many thanks!