In these devices which plug directly into the wall, the high voltage area of the power supply usually ends in two wires that supply 5 volts or 3.3 volts to the rest of the router. So you can power up the unit safely while it is open by supplying a low voltage to that point instead of connecting to line voltage.
To crack the case open without a vise I would try a C clamp or other clamp squeezing on opposite sides directly over the seam.
It's irrelevant what you want to call it, it can perfectly well be used as a router. The instructions you've been given in this thread are the same regardless of how you want to use it or what name you call it, so stop raging and take a breath.
That's not how a router is defined. At its basic, a router is a device that routes traffic between two or more networks -- you don't need DSL- or WAN-port for that, since it can e.g. happen over WiFi. The networks can even be entirely virtual and it'll still be routing.