Note: this tutorial assumes a basic familiarity with LNZ Pro.
When making a hexed breed, it's useful to be able to see your breed as an adult in the Adoption Center. By default the pet will come out as a puppy or kitten. You can age them up using PetzA's brain sliders, but to save yourself the trouble you can also set the breed to always come out looking like an adult whenever you select it.
For this tutorial I'll be using the in-game Great Dane breedfile, but it will work with any breed. Here's the Great Dane as it normally appears at the AC as a puppy:
Open up LNZ Pro and go to the main LNZ file. If you aren't sure where to find it, see my Tour of the Breedfile in LNZ Pro tutorial.
A tour of the breedfile in LNZ Pro
Scroll down to the section header [Little One] - it will normally be near the top.
Remember that a breedfile has two LNZ files - the adult and the puppy/kitten. The adult file is larger, whilst the puppy/kitten contains overrides to make the baby pet smaller and cuter. The Little One section in the adult LNZ file, which we're looking at now, tells the game where to find that baby stage info. To make your pet always look like an adult, all we need to do is point this section to the adult LNZ file instead.
In the original game breeds, the puppy/kitten files start with the two letter code for the breed (here "GD" for Great Dane) and then "pup/kit" depending on whether the breed is a dog or a cat. Remove the "pup/kit" part so that you just have the two letter code, which is the filename of the adult LNZ (which you're editing right now). Remember to keep the .lnz part of the filename, or the game won't know what file to look for and throw an error.
Save the file and take out the breed you just edited. It should now look like an adult:
Great Dane coming out of the AC with adult appearance
Note that this is just a cosmetic edit. The game will still consider your pet a puppy/kitten if you adopt it, it will make puppy/kitten sounds, and it won't be able to breed until a few days later when it grows up. The only change we've made is to make the pet look like a fully grown adult at all life stages.
Once you're done editing the adult stage, you can reset the [Little One] section to point to the puppy/kitten LNZ again.
Hint: You can use this technique to make "no grow" petz that always look the same!