I'd certainly be willing to help.
Really, with the roster files all that matters is that there be a lot of skin choices (is there a max number?) and then have almost all end with certain cfg dates.
Alternately, all the "civilian" schemes could be given pre-war cfg dates. They'd have to be specifically chosen in the campaign then to show up, unless the campaign used default cfgs.
IJN paints:
Looks like most prewar schemes had all black hulls (with stripes, etc). Some have a hinomaru on the side, too (I tried that once myself, hard to do).