Because I can (did I say that already?)
What is highlighted in FLASH block 0x45000, offset 8E0, is the instruction that loads a constant value 0x0003FC01 which is the speaker volume constant... The larger it is, the lower the volume is (it's a divisor).
I've modified my personal version of the software to be able to load any EXE block, allow edits and write back the changes - here I've made the constant 0x000AFC01 which is almost 3 times larger, and those disturbing chimes are now one third the volume.
This was in firmware AR79-14C026-AH (the latest) and the offsets will be different for older firmwares, and I'm not really going to be able to make this automated for any other firmware because of that. But enterprising persons may be able to create their own vbf file (with recalculated checksums) to have their own firmware version that doesn't scare the bejesus out of people in the car when a chime goes off.
That very well might have been the last item on my todo list.