If I am not mistaken, for the firmware HL23446 the vendorID variable can be altered by editing the /etc/init.d/sys.sh file
# override uci variables
oem-generic)
uci set sys.target.name=oem-generic
uci set sys.features.mib_customized=1
uci set sys.features.igmp_fast_leave=1
uci set sys.features.dying_gasp_enabled=0
uci set sys.features.suppress_power_level=0
uci set sys.features.eeprom_sync_option='1'
uci set sys.mib.vendor_id='ZM\0\0'
uci set sys.mib.ont_version='SFP-P05\0\0\0\0\0\0\0'
uci set sys.mib.equipment_id='GPONSTICK\0\0\0\0\0\0\0'