I believe you can write the command suggested by weidong.sun in your conf file and make it a part of rootfs through your yocto. Then it will be part of your image and no need to manually run any commands.
As I already mentioned in my previous comment, please go through below link thoroughly to add a new file to your rootfs. (Please read all the comments of the below link as well)
I am not want make custom layer,I just make some linux kernel driver to module and then when boot systemd add this ko,so I need to add conf file about my ko add into /etc/modules-load.d/
I refer the galcore ko it is the gpu driver but I can find make galcore.conf in code,do u know it?