there are some, particularly turret upgrades, but i didnt save the urls while i was reading them months ago because i didnt think anyone would need them. if i find them ill post them. but the below would serve as a good example itself, queen elizabeth class bships receiving major upgrades in between 2 world wars :
http://en.wikipedia.org/wiki/Queen_Elizabeth_class_battleship#Between_the_Wars
also florida class us bships :
http://en.wikipedia.org/wiki/Florida_class_battleship#Machinery
I think the interwar upgrades of some BBs was largely driven by the naval treaties - which basically stopped new BBs being built for c.15 years. The major navies really had no choice - if they want "better" BBs they were forced to rebuild the old ones.
In my view this is completely different to "upgrading" of secondary systems in HOI.
If you look back at the naval construction programmes in the early decades of the 20th century the upgrading took place as each class of battleship (pre and post dreadnought) was an incremental improvement on the previous one. All the effort was on new and better - there was no effort put into upgrading older units (until you get into addition of DP weapons etc later on - post WW1 - after the majority of the units were scrapped).