@Sachariase6 hi, it's me again, cake's source, here's my dank guide step-by-step:
1) acquire the best drawing tool if you hadn't acquired it yet - the Paint.NET
2) Open your 132 PlayerSkinsEmbed sprite sheet and 48 PlayerSkinsMaskEmbed sprite sheet with Paint.NET
3) press CTRL+SHIFT+R inside 132 PlayerSkinsEmbed sprite sheet
3.1) change height to whatever you want (e.g. i set to 5000)
4) press CTRL+SHIFT+R inside 48 PlayerSkinsMaskEmbed sprite sheet
4.1) change height to the same number that was set in step 3.1 (e.g. i set to 5000)
5) you may notice white spaces if you zoom out of your sheet, that's normal, to remove the one in the bottom find the "Magic wand" instrument (or press S letter 4 times), and with it click in the middle of the bottom white space and press DELETE.
5.1) repeat step 5 for another sheet
6) to remove the one at the top you must press CTRL+A and move the whole thing straight up using the "Move Selection" instrument (or press M letter once) UNTIL the bandit rogue skin hits his head
6.1) repeat step 6 for another sheet
7) Press CTRL+S in both sheets
8) Replace your edited 132 PlayerSkinsEmbed sprite sheet and 48 PlayerSkinsMaskEmbed sprite sheet in JPEXS
9) Rebuild your client
10) CONTINUE ADDING YOUR SKINS
1) acquire the best drawing tool if you hadn't acquired it yet - the Paint.NET
2) Open your 132 PlayerSkinsEmbed sprite sheet and 48 PlayerSkinsMaskEmbed sprite sheet with Paint.NET
3) press CTRL+SHIFT+R inside 132 PlayerSkinsEmbed sprite sheet
3.1) change height to whatever you want (e.g. i set to 5000)
4) press CTRL+SHIFT+R inside 48 PlayerSkinsMaskEmbed sprite sheet
4.1) change height to the same number that was set in step 3.1 (e.g. i set to 5000)
5) you may notice white spaces if you zoom out of your sheet, that's normal, to remove the one in the bottom find the "Magic wand" instrument (or press S letter 4 times), and with it click in the middle of the bottom white space and press DELETE.
5.1) repeat step 5 for another sheet
6) to remove the one at the top you must press CTRL+A and move the whole thing straight up using the "Move Selection" instrument (or press M letter once) UNTIL the bandit rogue skin hits his head
6.1) repeat step 6 for another sheet
7) Press CTRL+S in both sheets
8) Replace your edited 132 PlayerSkinsEmbed sprite sheet and 48 PlayerSkinsMaskEmbed sprite sheet in JPEXS
9) Rebuild your client
10) CONTINUE ADDING YOUR SKINS