So... I feel dumb. I was overly worried about making it so that a power source could be plugged in without the battery also supplying power... I realized earlier that the battery is in line with the power source because duh how else are you going to charge the battery... So that was a waste of thinking... So this simplifies the plug in console idea considerably and I don't need to imagine kill switches that force the battery to be disconnected before a power source can be plugged in... I'll just see myself out. Now I just need to desolder the double USB ports and replace it with a lovely single USB wired to where I need it for positioning and figure out the HDMI port.
HDMI takes precedence because I really don't want to try desoldering that... yeah. A quick google search later and I'm convinced. 19 freaking data lines, smushed really close together... I'll leave that alone. I was micro-miniature repair certified once, but there is no way in hell I'm going to risk it on a part I own until I am a little more financially able to replace said 40 dollar board. USB is much nicer, 4 to 8 connections with enough room to work with. I believe the power converter even came with a single USB female port, which I could wire around to wherever I have enough space.
Really need the case to get in so I can put in the pieces that MUST go in a certain spot like the monitor, HDMI port, and controller board so I can see where I can fit in the battery, audio amp, power booster, charger, volume knob, etc. Glad it's a DMG gameboy, should have plenty of room to work with once I remove excess plastics for battery compartment and unused posts.