would add the same amount as paint, although have you seen the thickness of the sheets they use? I doubt it will make a noticeable difference, even then you can talk too them about removing paint-film that gets on the inside if your really need too. I would just recommend contacting the place you plan having do this to your gun and ask them.
"The M98 is not a particularly light gun, on the other hand it also feels tough. Most light guns feel like cheap toys, the M98 feels like a serious weapon of war. If you can't take the weight, play a new sport." - Jesus 1st CAD