[yocto] Proper way to edit bootimg - image

[Teemu K]

Hi,

I have created image for x86 -based hw with Yocto 2.5. Image is using
bootimg-pcbios that is then mounted to /boot when image is running.

I now need to modify that bootimg that is mounted in /boot. I think
it's created by scripts/lib/wic/plugins/source/bootimg-pcbios.py -
script.

What would be proper way to to modify the bootimg or does it has to do
with modifying that bootimg-pcbios.py - script?

-Teemu Keskinarkaus