Im going to explain a easy way to keep your saved games working when there is a update.

First, you must edit your \Documents\Paradox Interactive\Hearts of Iron IV\settings.txt and set "save_as_binary=no".
Every time you start a new game, backup the mod version: search for bicemodded.zip under the Steam\steamapps\workshop\content\ and copy it anywhere to keep it safe.

Now, when a update comes out and the game doest not recognize your save, here is what you do:
create a new game with any country and save it. Now open up in a txt editor your new save and the old save.

Theres gonna be some stuff like this:
-------
Old save:
-----
HOI4txt
player="♥♥♥"
ideology=fascism
date="1943.11.1.1"
difficulty="normal"
version="Cornflakes v1.5.3 (fddb)"
tutorial=no
player_countries={
♥♥♥={
user="xxxxxx"
country_leader=yes
}
}
save_version=7

-----
new save:
---
HOI4txt
player="ENG"
ideology=democratic
date="1936.1.1.12"
difficulty="normal"
version="Cornflakes v1.5.3 (6ec8)"
tutorial=no
player_countries={
ENG={
user="xxxxxx"
country_leader=yes
}
}
save_version=8


------

Now, you o copy the "version" and "save_version" from the new save to the old save.

So you have this:
---------
old save edited:
-------------

HOI4txt
player="♥♥♥"
ideology=fascism
date="1943.11.30.7"
difficulty="normal"
version="Cornflakes v1.5.3 (6ec8)"
tutorial=no
player_countries={
♥♥♥={
user="G.Kothe"
country_leader=yes
}

}
save_version=8

----------

Now, to avoid possible in game crashes, caused by the update itself, you replace the bicemodded.zip with the one you copied the first time when u started the game (the older version of the mod).
Probably you should do this step everytime you gonna play, because steam may update your mods at random times.


Maybe your not gonna be able to recover your old saves now, because of the first steps which are required to be done before a update. But now you know how to prevent it for future updates.

I tried it once today, and i was able to open a older save.