As we know dutch warships prior to and during WWII (or at least the early parts of) were prefixed by Hr. Ms. (as in Hr. Ms. Java for instance).
Some time later (post war?) that prefix changed to HNLMS.
When, that is approximately what year, did that change take place?
Thanks for any help.
The change never happened. The Dutch pre-fixed was and continued to be Hr.Ms., which is the Dutch abbreviation for Harer Majesteits, which translates to Her Majesty's.
This only changed when Willem-Alexander ascended to the throne in 2013, and pre-fixes changed to Zr.Ms. (for "Zijner Majesteits", which translates to "His Majesty's").
The English translation would be HNLMS in both variants, but this is a translation, not an official prefix for the ships. I also found HNMS on occasion but that would create an obvious risk of misunderstanding, because Norway also has a monarchy and a navy.
See more here:https://marineschepen.nl/dossiers/hr-ms-en-zr-ms.html