Most times, we do NOT recommend completely disassembling front calipers because the two flat o-rings that seal the caliper halves are not generally available and are not included in rebuild kits. So you are forced to reuse the old OEMs which is not a good idea. Round o-rings will not reliably substitute, either.Use Girling brake component grease on the flat o-rings during reassembly, and hope for the best.
At the same time, powder coating requires heat of 350 degrees F or more, which is not good for rubber if you don't separate the halves. Interestingly, Wilwood, Porsche, BMW and a host of other manufacturers say the same thing about not splitting their two-piece calipers. Do LOTS of testing for leaks under high pressure after putting the system back together. Brake mods are serious business.