Is There A Way to Shape Stuff in GIMP?

[Oddonelynx]

I want to make a realistic preset of a pitbull terrier! But, I have a little problem.

The head doesn't fit in the guidelines. Is there I way I can deform and mold it into the guidelines? If so, please tell me  how!
The cage tool doesn't seem to do the job for me.

[Bawfle]

I'm afraid it's something only good photo-shopping can do since you'd have to fit all the realistic proportions into the FH model proportions...

It might help to copy and paste different sections of the dog's head and fit them into place first? Muzzle, head, nose, eyes mainly. With the FH model though you're not gonna get that lower lip flap since the FH model has a wolf muzzle, completely different to the breed you have there so I imagine you might have to raise the muzzle in the image to the UV map line and create a jaw or something!

Using the fix or patch tool should help too! I think it would look like a band-aid? Using that to create fur/skin in empty areas would help a lot. Maybe look up some tutorials on how to do that! But unfortunately there's not much else to say or offer advice with other than asking a map maker who has had experience with doing similar things.

[Oddonelynx]

Okay, I'll try that Bawfle, thanks! (That's the feline UV by the way.)

[Samue]

The Warp Transform tool can shape things. Before Gimp version 2.10 it was called iWarp and was in the Filters tab (near the top of the window) under Distorts and worked a little differently. You can use it to move pixels, grow an area, shrink an area, swirl parts of the image, and a few more things (in Gimp 2.10 or greater the place you change those settings is right above where you`d change the size of your brush).
You`d probably want to scale up the image before using the tool, though. You can scale it using the scale tool.

If the dotted yellow border that`s visible on the picture you posted cuts anything off then you can click on the layer it`s on then go to Layer (near the top of the window) and click on Layer to Image Size and it`ll stop cutting things off.

If you select something you can move it by holding down shift-ctrl-alt then hold down left-click and drag it around (only let go of shift-ctrl-alt when you`re done moving it).