sort of! 

ok, it's like this.

forget about Hexagon.  just focus on exporting and importing your morph.

let's say you apply Random Full Body Morph X (FBM X) at 100%. 

then you export the chest as Chest Morph Y.

then without making any changes, you import Chest Morph Y into the chest of your figure.

let's say you have FBM X still applied to your figure.  importing Chest Morph Y morphs the chest to 100% of FBM X.  FBM X is also morphing the chest to 100%.  so you're doubling the effect of FBM X on the chest.

now, FBM X affects lots of body parts.  you don't want to dial them in manually.  so you want to select the chest, and dial the equivalent chest morph to negative the amount of FBM X in Chest Morph Y.  in this case, that means dialing in -100% FBM X.

so, in your specific case, every amount you dial into the Full Body Morphs that has an equivalent in the chest and gets exported in the morph needs to be dialed in negatively in the chest.  if you have Young 0.5, Toned 0.4 and Thin 0.2 dialed in the Body (sorry, i don't remember your actual values), export the chest with those morphs included,   make your correction in Hex, and then import the corrected morph to the chest, you need to dial Young -0.5, Toned -0.4, Thin -0.2 on the chest.

you aren't actually following the tutorial precisely,  because it's starting with the figure at default.  though skimming it, i don't see that mentioned as a requirement (and it really should be).  because you're making that change, you need to change the process accordingly.

the thing to remember in this process is that your custom morph has lots of other commercial morphs in it.   this prohibits you from ever sharing or selling your custom morph with anyone else.  otherwise, you'd be distributing other people's work.   so if you catch the Hex bug and find you really enjoy making morphs, you have to work with the figure fully at default. there are other intellectual  considerations for distribution as well, but i think that's beyond this discussion.

does that help at all?