So; it's so:
I boosted BaseSystem.dmg with the Production boot.efi from Pike's github, added the modified Distribution to OSInstall.mpkg, modified the InstallableMachines.plist, and centralized all with the Production boot.efi in an easily-accessible location from which I could copy all to their respective places in the createinstallmedia Installation environment . . .
I was able to successfully cp everything but the boot.efi (/ is persistently ro, no matter what I tried) over via terminal in said environment, but--upon closure of terminal--the Environment becomes un-responsive (I tried something like five times to no avail) ;(
The createinstallmedia route made me mad, before, but it's pissin' me right-teh-fsck-off atm!
I'm'a gana' try once more, Pike, but after that I'd best call it quits with createinstallmedia before I blow my personal, internal, power supply