I know most of the experienced modders know this already but there are a lot of new modders here so I hope this helps some.
Open png file with 7zip then drag the "appearance_info.RDAT" to desktop or folder of your choice
Edit the "appearanc_ info.RDAT" with Notepad++
For shoulder width look for "rightArm.ty":and "leftArm.ty" - Change both to same number
*****Make sure there's always a (,) after your number Example (15.0,)******
For arm length look for "rightHand.ty": and "leftHand.ty" - Change both to same number
For short arms use (26.0,) and for very long arms (29.0,) but you can adjust to your liking
For body length look for "spine2.ty":
Increasing the number shortens the torso and lengthens the leg appearance. Decreasing the number lengthens the torso and shortens the leg appearance
For neck length look for "head.ty":
Increasing or decreasing the values will change the neck length
How accessories fit is controlled by below items:
"forearmTHIN": 0, self explanatory (If too loose increase value/If it clips decrease value)
"forearmTHICK": 0, self explanatory (If too loose decrease value/If it clips increase value)
"upperarmTHIN": 0, self explanatory (If too loose increase value/If it clips decrease value)
"upperarmTHICK": 0, self explanatory (If too loose decrease value/If it clips increase value)
"trapTHIN": 0, self explanatory
"trapTHICK": 0, self explanatory
"neckTHIN": 0, ?
"neckTHICK": 0, ?
"chestTHIN": 0, how tight or loose jersey fits around upper chest area (If too loose increase value/If it clips decrease value)
"chestTHICK": 0, how tight or loose jersey fits around upper chest area (If too loose decrease value/If it clips increase value)
"breastTHIN": 0, unused (for female png's I assume)
"breastTHICK": 0, unused (for female png's I assume)
"absTHIN": 0, how tight or how loose jersey around waist area
"absTHICK": 0, how tight or how loose jersey around waist area
"headTHIN": 0, ?
"headTHICK": 0, ?
"shoulderTHIN": 0, how tight or how loose jersey around outter shoulder area (If too loose increase value/If it clips decrease value)
"shoulderTHICK": 0, how tight or how loose jersey around outter shoulder area (If too loose decrease value/If it clips increase value)
"hipsTHIN": 0, how tight or how loose shorts fit around waist area
"hipsTHICK": 0, how tight or how loose shorts fit around waist area
"thighTHIN": 0, how tight or how loose shorts fit around thigh area (If too loose increase value/If it clips decrease value)
"thighTHICK": 0, how tight or how loose shorts fit around thigh area (If too loose decrease value/If it clips increase value)
"calfTHIN": 0, how tight or how loose socks/leg accessories fit (If too loose increase value/If it clips decrease value)
"calfTHICK": 0, how tight or how loose socks/leg accessories fit (If too loose decrease value/If it clips increase value)
The best way to judge how the accessories should fit is to find a player model of similiar size and copy the values and play around with them until you
get the results you like.
Hit file then save. Open 7zip then drag the edited "appearance_info.RDAT" from desktop to open 7zip
Copy the edited png file into you modded folder and you changes should appear when you go to edit player.