Is this correct? If so, how can I add some boot parameters to it?
The cmdline parameters are hardcoded into the kernel, namely by the kernel config:
LibreELEC-AML/linux.arm.conf at master · dtechsrv/LibreELEC-AML
'Just enough OS' for Kodi for some Amlogic TV boxes - LibreELEC-AML/linux.arm.conf at master · dtechsrv/LibreELEC-AML
github.com
But kernel also loads the initargs variable into the cmdline, so if you add what you need, it might work.
Read initargs variable:
You can change it with this command:
The ... means the original value, the whole string returned by fw_printenv | grep initargs.
I think what comes next is quite clear: variable=value.