Unfortunately, it's a little more complicated than just swapping out the current "master controller" for another PID. OP would need to add at least two alternate PIDs, one for the HLT and one for the BK. Would also need to add a temp display for the MLT (could be another PID.) Would also have to add pump switches, as the pumps are also controlled by the master controller. Same for switches to control the "element enable" contactors. More additional components would be necessary to mimic some of the other functions supplied by the existing master controller.
Unfortunately, the OP is being affected by one of the risks of buying customized equipment from a small (one man operation in this case) business. If the supplier goes away for any reason, and your equipment fails, you might end up with an expensive doorstop.
Brew on