I think it will overwrite the params partition (one of the device specific partitions of your device) and of course softbrick it! 
Without backup. 
initramfs.bin images should be used through serial access in U-Boot, and not for TFTP recovery!
Yep, those initramfs-kernel.bin files should be wiped from the "Firmware OpenWrt Install URL" column!
Leave it empty and let my builds noted in other sections of the page.