I have no idea when or even if USD over offered factory training on DH regs. I have an old service manual written by the Scripts Institute for servicing early DA's. It's interesting to me since it has drawing and specs of tools necessary to service the reg.
I personally would not rechrome it unless you just have to have a shinny new reg, the old battle scars give it character
Chroming is an involved process. I am far from an expert ....wish Dave was around, he is a master at it....but as I understand it, to be done correctly, the brass has to be totally cleaned and polished, plated in copper, then nickel and finally chrome.
As a side note, take some time to research DH diving. While not difficult, they are different. Hose recovery, hose clearing and sharing air are unique to DHs. Then there is the choice of BC.....or no BC for that matter. While any DH will function with any BC, using the wrong BC with a DH will result in it not preforming well. Many of the claims of poor performance of DH regs is due to improper BC and diving technique rather than the reg itself