Not sure about switching a full set of modules between a crewman and executive but it should work in theory.
If your mechanic is telling you that you need to replace coil packs or if your vz is doing dicky things like not opening or staring intermittantly, throwing multiple sensor faults, especially when the car is hot, try cleaning out the ecu connection lightly with compressed air and checking the terminals for corrosion or oxidisation before you go down the road of throwing parts or replacement modules.at it.
I had the same problem with my vz's a few years ago. (I was running a fleet of 4 as work vehicles)
Each ecu has a code on it which corresponds to the bcm, pim and key. From what I can remember, there are 20 something different codes and gazillions of key combinations. I bought used bcm's with matching codes that were reset but each time I had to get a Holden tech to reprogram them....and then I had to get my locksmith mate to reprogram the spare keys. All of this ends up super bloody expensive!
A good option is to use a full set of ecu, bcm, pim and keys from a donor (I was paying about $600 + freight a set) but as Tazzl said...you can't be sure of:
a. They work
b. They will last
AND, as most wrecks will only come with one key, you will have to pay for a spare key that's coded by a locksmith. All of this gets full on exxy when you have to do it more than once and on more than 1 vehicle!!
Tazzl was right....the ecu's get hot! and mounting them on the front of the engine is the stupidest thing ever!
After I'd been down the same road 4 times, I came up with the idea of making a shield that sat behind the ecu to shield it from the heat from the engine. I'm a leccy, so I used the back of an old switchboard (yes, it's asbestos) cut to be about 50-60mils bigger than the ecu each side...with a lil bit of tweaking to make it fit and longer bolts to hold it in place....never had a problem again!
They all got traded so I can't attach a pic, but if you come across any white ve wagons with the ecu mounted on a small sheet of fibre board...that was me! lol
I now run a 2010 SV6 wagon and I'm starting to notice that it'll throw weird fault codes, that don't log (ie. don't show up when you plug in a scan tool), when it's hot, wet, dusty or if I've given it a flogging.
The ecu is mounted away from the engine block (Holden learned a lesson), but its off to the side of the engine bay and still gets exposed to heat, dust, moisture etc. I'm in the planning stage of making a box or shield for this.....I'll keep you posted.