If I change code signing certificate. I need to update signatures in update-0.95.properties file of all of previous update files, so they can be validated on download, right?
If i do so, then when I start the client with older version it's old files will not be validated because they have different signature and fromVersion will be null (broken download). So it will start initial download instead of partial update.

$> javaws game.jnlp
Integrating old updates and looking for new ones
GAME: game
Validated /home/zlaja/.config/game/jar/game-0.95.1.jar: false
Initial Download triggered by the following missing classes: java.lang.ClassNotFoundException: games.stendhal.client.stendhal
Update state: INITIAL_DOWNLOAD initialDownload: true fromVersion: null

Or I just need to update signatures of new files? Is it possible not to update signature of old client game-x.xx.x.jar files that hold version information. And update signature of all other files which needs to be downloaded for partial update. So update manager can check old version and validate needed update files on download. Now, as I can see, it checks all files in load-0.95= section of jar.properties file. And if some of them has wrong signature it considers it broken download.