"The Fuselage modifier is outdated, you need to replace it with a new one." error

Yeah! it's gonna be marginally better than having to rebuild all the parts. But still better I guess. You could operate under the assumption that ANY "version" number that's not equal to "VersionLast" will cause issues, then check all parts! But prolly worth noting this is not a better work around then having the ability to just "update all parts to current version" (if that were an option available). Just the best option available at this time!

@Toinkove I just went to try that and... The "funny" thing is that in sandbox mode, you don't get anything in the error/warning panel so you don't really know what parts are causing the issue. I guess you could manually make a list but since the error/warning panel only lists up to 50 items then... Yeah. It's doable, but not as straight-forward as I thought.

@Toinkove That's wonderful. That's a lot better than rebuilding the parts. Adjusting for performance shouldn't be that big of an issue (in my case).

Sorry it's "Version" then "VersionLast" ..... and it's on multiple pages but most are all same except on one page. Basically just want to make sure "Version" is the same as "versionLast"

@HarlockG
ok my previous suggestion does not work but I found something that does. You'll have to do this in sandbox mode but, go into the tinker panel and click on "edit hidden properties". On one of the screens that appear you will see something labeled "version number" at the very bottom of the list. The part will say Version: 1 then Version: 2 bellow that. Make sure both are set to Version: 2 then "apply" that change at the top. This should convert the part to current modifiers without having to get a new part and go through all that! just know the vehicle may not perform the same as originally designed with the new changes.

Sometimes if you change a parameter (like on interstages, changing to Soyuz style then back to normal) this might trigger it's modifiers to the newer parts. At least that used to work for some parts they changed in the past!

@Toinkove Yeah I've just realised it happens to some detachers as well. Would be awesome to auto-convert with the new properties, instead of removing, adding and resizing each replacement part.

It means they changed a lot of stuff on the parts (mass, price, etc). One example is: I noticed the interstages got quite a bit heavier! (the struts seem to be a bit lighter though) Anyhow career mode doesn't allow for these older parts I guess for balancing issues. It will also mess up a lot of stuff. I managed to get one of these craft launched somehow and the amount of fuel I needed to orbit Luna almost doubled throwing off my whole mission so. Beware!