Quote - ...Do i have to re-apply the new torso texture with the tattoo to ALL zones?

No, you do not.

When you apply a texture to a material, that texture gets loaded with the model. So, if you apply a new texture to the Chest material and keep the old texture on the Torso material, BOTH textures will be loaded on the model in the Preview pane and during rendering.

However, it is generally good practice to keep the textures consistent, as they are intended as mapped. The reason for this is memory - If you had separate 4000x4000 texture images for every material, all of those would get loaded at the same time.

High resolution textures can take up a ton of memory when you're loading up several of them. Instead of just one 4000x4000 texture, you could have several or many, all loading up at the same time, reducing your machine to a crawl.. If that's not necessary, limit the amount of memory needed by just doing good "bookwork" and loading up as few textures as necessary. That's why it's common practice to change all the textures across material zones, if they all normally call and share the same texture image file.

Quote - ..Right now i'm just adding the torso texture with the chest tattoo to the chest area only, and leaving the old texture in the other material zones. Could this be what is corrupting my morphs?

Textures won't blow out your morphs, unless you're talking about some displacement or bump map problems.

But, you could end up with a model that is so memory "heavy" that strange things could happen. I find that hard to accept, given that if you can run the software, one model probably wouldn't do it unless the textures were absurdly large.

Another thing - Morphs take up space, too. In many ways, they're just like real geometry and have to be loaded as well. (In Poser.) You don't see them rendered, but the data is there, regardless, and takes up space.

It's "feasible" you could have memory problems that could cause your issue, but it's very, very unlikely they'd be caused by your texture manipulations. (I don't know if it's even possible, since I don't know how the program would deal with that sort of memory problem. Likely, it'd dump the textures first, though.)