Adjusting the Character Mesh after Rigging

after you’ve skinned a character, you might need to make adjustments, either to the character mesh (for example, adding details such as pockets or increasing mesh resolution for more realistic-looking joints) or to the rig, such as modifying the structure. This section shows how to recover from such a situation without having to re-skin the character.

https://knowledge.autodesk.com/support/3ds-max/getting-started/caas/CloudHelp/cloudhelp/2016/ENU/3DSMax-Tutorial/files/GUID-A44FE485-78AA-4BE3-AC7E-9ECFEC5FBDFD-htm.html