Does Buying and Enabling a new DLC in Europa Universalis disable an ironman save?

Solution 1:

I'm afraid all old saves previous to the 1.12 patch (which will be released in line with the Common Sense DLC) will be broken and unplayable.

Apparently this patch will be quite a large overhaul. To play you're old saved games you're probably going to have to elect to run EU4 in a previous version within Steam. Or set it to not Auto update.

But then because you're running in an older version all the nice new features in the new Dlc will be unavailable to you.

See this Reddit post

Usually the act of enabling a Dlc will not disable an Iron Man save. However the larger Dlc's are usually released along side large patches. It's the act of upgrading to these new patches which can and often do break old saves. Dlc's which have already been released and minor Dlc's such as music / flag / graphics packs aren't an issue.

However as a side note the use of certain Dlc's are known make Iron Man mode saves ineligible for steam achievements. Such as character designer in Crusader Kings 2.

Solution 2:

It will not work and if you try to load it you can ruin the save!

However, in Steam, you can re-roll to older version of EU4 (Properties - Betas - Select Beta...) and continue playing your old saves. You just need to remember what save is for what version.