Herelink OEM run at boot

There is a nice explanation for creating an OEM image, but currently I want to run a simple(linux based c program) on the Herelink. I have done this in the past using root and hijacking for example system/bin/ to run it a boot, since the root folder wasn’t writeable.

But now without root how would you approach this? The program I want to run is similar to for example ‘mavlink_router’ and is extremely simple and already did run on the beta versions.
Ideally it would be nice if I place a /oem/etc/ it gets run at boot.

Next to the ‘run at boot’ is there also a way to enable the wifi tethering at boot and maybe configure the accesspoint name/password with the oem image?

you could sideload an app like this

Thanks! Is there also a solution to run a simple program at boot, like adding a /oem/etc/ or a way for me to regain root access?