I know, I know...I've become quite the necromancer.
There's a program contained in the latest download referenced in this thread, called isocpy.exe. This program is called by a simple batch file, with commands like:
isocpy ..\MENU\EQIPMENU.MNU D:\SLPS-01057.bin 53992
I assume this command would copy EQIPMENU.MNU (currently residing one directory up, in the adjacent directory MENU) into the disc image SLPS-01057.bin, at LBA 53992, presumably over the top of whatever previously existed in the space required.
If this assumption is correct, am I to understand that, if so inclined, one could use this program to insert files into disc images at specified LBA? I realize there are other apps out there that can also do this CDMage, CD-Tool, etc), but as this seems like a very simple tool, it would eliminate confusion related to configuration, settings, etc.