There is no 'coding' as such of the rear brake modules - the Discovery Sport (L550) has a motor on each caliper, the current is controlled by the ABS block and the current flow direction swapped to power the park brake on or off. The only calibration needed upon replacement is to store the current draw for each motor & direction in the ABS - a twenty minute job.
I would suggest that there may be a wiring or connection issue causing the calibration to fail. If this is the case, then it will rear it's head again - hopefully not with the park brake applied....
It would be useful to know what diagnostics they were using, if it's of the same era as the invoicing software, then It's no surprise they struggled. I'd also question which parts they change exactly - the park brake motors are available separate to the calipers and obviously cheaper.
Not all independent tech's are 'the best thing since.....' just as not all dealer tech's 'just follow what the computer says'. I've worked in both environments (currently indie) and there's a full range of awful to excellent in most workshops. The best thing I can suggest is try and see the condition of the cars the tech's drive - if they're snotters, then why would they care about your car and not their own?