How to stop SoI member from being annexed as a result of offensive war?

[Cossack_PL]

I'm playing France, used Left Bank decision to DoW Prussia, freed Rheinland and took Prussian Palatinate, which I gave to Rheinland too by save editing (it's also their core). My problem is that about one year after the release, Rheinland DoWs Hesse-Darmstadt over their province with Rheinlander core (Mainz IIRC). Then Prussia as SoI leader joins, while I cannot, because it's an offensive war and Rheinland didn't call me to arms, even though we have an alliance. Then Prussia adds their wargoal to annex Rheinland, which would destroy all my effort from the last war.
Is there any way to avoid it other than releasing Rheinland as my puppet?

 

[Liborio]

Ally them and pray they will call you. No other way (that doesn't involve using the console) i'm afraid.

 

[Maggix]

I'm playing France, used Left Bank decision to DoW Prussia, freed Rheinland and took Prussian Palatinate, which I gave to Rheinland too by save editing (it's also their core). My problem is that about one year after the release, Rheinland DoWs Hesse-Darmstadt over their province with Rheinlander core (Mainz IIRC). Then Prussia as SoI leader joins, while I cannot, because it's an offensive war and Rheinland didn't call me to arms, even though we have an alliance. Then Prussia adds their wargoal to annex Rheinland, which would destroy all my effort from the last war.
Is there any way to avoid it other than releasing Rheinland as my puppet?

IIRC you can intervene as soon as Prussia adds the wargoal and the warscore is below 0 for Rheinland.

 

[maxirage]

You're out of luck. The AI only calls allies on the first day of the war, and you can't interfere in an offensive war. They didn't call you probably because you have a truce with Prussia, but they didn't directly attack Prussia, so it couldn't account for it.

 

[Soviet Onion]

Load the save as Rheinland, call France to the war, and immediately use the console to tag-switch to France. Accept the call to war. Done.
If you have a truce with Prussia, you can probably edit the save game to remove it.