I got this helmet a few years ago directly from Japan and although it was sold to me as a WW2 Japanesearmy helmet after I got it, without me doing anything to it, it morphed into a WW2 Japanese civil defence helmet. However, I also purchased a number of Jap canteens at the same time and I was able to "do a deal", as a certain US president might say and, therefore, I got the helmet at a fair price even if is civil defence rather than army.
I think that this helmet has the lightest of light linings that I have ever seen on a helmet. One can imagine that if one had a brick land on one's head while wearing this helmet one might, possibly, have a rather sore head.
I don't believe that anything has really been done to this helmet since the end of WW2.