VKGAW41G is something OEM customized, i don't know for what WD is published it on support section, VKGNW984 is exactly what you need. In HGST fw files letterts 3 and 4 defines for what market drive intended. GN is generic.
nope, build date of this firmware is 07/01/21 13:33:28. Open fw in text editor and just search "codf"
Here many of updates HDD Firmware Downloads. PC-3000 Support Downloads. Data recovery and HDD repair tools
Don't do this! Firmware stored not only in flash, it also have program code on platters. Firmware update, when applied properly, it modifies different system modules that stored in flash an on platters