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queef-face I figured out a work around and I can't believe I didn't figure that out sooner. You simply have to press the right-most button below the cropped image. I advise editing the image with another software beforehand because if you change the cropping in any way it will reset back to the "limited" cropping.
DannyPennis Firstly this is how imgXiwi converted the .iwi file: 
This is how I would place the image on the gun without altering the converted image at all (placed on the Remington writing) :
Now this is how the weapon looks like in game:
It's so weird I cannot understand why it does that at all. Note as well that the texture looks weird as hell too.
I know this is more than you asked for but I just wanted you to see my process. Maybe I am doing something wrong in between or something. If you would like I can share every click-by-click procedure as well but I hope for both of us that this won't be necessary.
DannyPennis thanks again for your support so far! I will try my best to look for videos or something similar and make it work.
DannyPennis is there any sort of tutorial somewhere on the world wide web or do I have to just "fuck it I'm free ballin this" (experiment myself and go through trial and error)
DannyPennis i took the weapon_remington_acr_col.iwi file and converted it into a png using imgXiwi.exe. Then I used paint.net (image editor software) to try and align the image on the weapon for example an image on the acr where Remington is written. I convert the new weapon png into a .iwi file and put the file where I got it from in iw_06.iwd (the new file has the same name as the old one so it is also called weapon_remington_acr_col.iwi). Unfortunately the alignment in game is nothing like I intended it to be.
DannyPennis But I don't see any iw4 folder. I see demonware (no clue what that is), iw5, t4, t5, t6. Do I just create a folder named "iw4" and inside that folder I create another one named "images"? Or place it inside iw5/images (seems to make more sense to me)?