`oom_score_adj` is inherited on fork, so you can set its initial value for new children by setting the desired value on the parent process.
Thus if you’re starting the target from a shell script,
echo 1000 > /proc/$$/oom_score_adj
will change the shell’s value to 1000, and any process subsequently forked by the shell will start with `oom_score_adj` set to 1000.