I play paintball and I carry an SP-8, big ole electric hopper filled with wholesome splat--tastic goodness. In addition to that...3-point sling, holo red dot sight, verticle front foregrip, mini-flashlight (I play night games as well), and a video camera (light weight made for extreme sports), add to this my air tank, two paint grenades, and 1,200 additional paintballs in loaders on my vest, handsfree radio, water camelpak...the importance of being in good shape is not lost on me.
I don't buy into modding a firearm will harm its performance...unless you are having an idiot do the work, ultimately the law of diminishing returns is in play.
As far as RAW goes...some rules are more worthy of being discarded than others you get to decide which ones make the cut.