Blaster modifications and safety in the context of HvZ

This document is intended as a reference for anyone who needs to decide what modifications to Nerf blasters (and similar toys from other brands) to permit in their game, with a focus on games of HvZ played on campuses. The purpose of this guide is to give people the knowledge that they need to make safe decisions without being overly restrictive. It was originally supposed to be short and concise, but it grew over time into, well, this. Safety is important, so I think it's worth taking the time to read. This may be of use to both moderators, who make the details of and implement a game's rules, and campus officials, who have the final say on what is permissible.

I've added pictures in an attempt to make this a little less wall-of-text-ish and to break up the sections; these images are from Steph Smith's pictures from the University of Waterloo's first invitational, this imgur album, Oklahoma State University HvZ Facebook page, more from the same facebook page, and toyland.gizmodo.com. All of the images you see here have been edited (trimmed and resized) by myself.

EDIT: Almost immediately after publishing this  post, a conversation started on reddit regarding the use and safety of Chinese LiCo batteries such as Trustfires - which has been a matter of some controversy over the years in the Nerf and other hobby electronics communities. I may have been overly generous in my assessment of the safety of these batteries, so I've edited the post to correct this.