possible to swap ecu 2004 subaru impreza?

Hi,
Noob's first post here, but I've read a bunch trying to figure out the answer to
my Subie's problem. Please point in the right direction if this is already
posted elsewhere - thanks!
Vehicle: 2004 Impreza RS 2.5, SOHC, no after-market enhancements, about
100k miles

Due to a series of troubleshooting events under the hood I now have a PCM
/ ECU that has an open ground running to the AC Compressor. I have a
trustworthy shop that has diagnosed this and all signs point to this
unfortunate self-inflicted problem. Of course, I also need to replace the AC
Compressor, Receiver Drier, Therm switch, etc.
The shop recommends replacing the ECU / PCM, which as you know is quite
expensive. I've been looking into ECU swaps here, but I can't seem to find a
definitive answer. I'm just looking to get my blue bomber back on the road
while not spending more than the car is worth to fix it.

Q1: Can I swap out the current ECU / PCM for an undamaged one from a
'retired' Subie of same exact year and model? 22611 AH522
Q2: Or, is it possible to fix the one I have because there is only one problem
with it?
The car still drives well, just no AC. I'm trying not to drive it for fear that other
electrical issues may 'creep' from this one. I read somewhere that '04 owners
are 'lucky' because '05 on swapping of ECU isn't possible.

I'm semi-handy under the hood, but obviously nowhere near an expert.
Thanks in advance for any advice.