by today's standard there are numerous things that are not up to the code, and the roof probably leaked several times during it's history. As far as it is not leaking now, your best option is not to mess up with it.
however, I do suggest you to tie the rafters pairwise on both sides. currently this is not done for each pair. given the minimal size of lumber used, this at least would increase the integrity of the structure.
I also see asbestos insulation in some degree of deterioration ( I believe it's asbestos), that you need to deal with soon.
