'Twas brillig, and the slithy toves did gyre and gimble in the wabe

Nah, I just added IF NOT !foo:~0^,1!==K (...) to the mess.

The full command was:
@for /d %I in (????) do @for /d %J in (%I\??) DO @for %K in (%J\*.jpg) do @(set foo=%~nK&& if not !foo:~0^,1!==K ( ( if !foo:~4^,2!==10 ( set bar=A) else ( if !foo:~4^,2!==11 ( set bar=B) else ( if !foo:~4^,2!==12 ( set bar=C) else ( set bar=!foo:~5,1!) ) ) ) && echo %K K!bar!!foo:~6,2!!foo:~20,4!.JPG && ren %K K!bar!!foo:~6,2!!foo:~20,4!.JPG ) )
It was used for bulk renaminmg of photos, as the default naming format from Kodak's software is pretty useless. I'd used exiftool previously to shift the metadata into the filename, but wanted to do some more formatting.

On a related note, do you know of a win32 touch equivalent that actually sets the creation datetime? All I've seen only handles modification datetime, and sometimes access datetime.