how to change system default setting by modify source code (or script)?

i want to change system default setting ,such as /etc/systemd/logind.conf.

it is:

[Login]
#NAutoVTs=6
#ReserveVT=6
#KillUserProcesses=yes

i want to enable some lines:

[Login]
NAutoVTs=6
ReserveVT=6
KillUserProcesses=yes

so i checked package.mk of systemd,but it don't change these lines.

i checked many files/scripts about systemd directory(packages , scripts,config,build.LibreELEC-xxxx-devel,projects....)

and i search logind.conf in all directorys and changed every file i found ,then recompiling ,but it change back at last.

there are so many system config files, i don't know which scripts or files to generate these config files and how they generate defconfig files.

what can i do to change this file ? or which files should i to view to find it how to work?

Quote from vpeter

After LibreELEC.tv/package.mk at master · LibreELEC/LibreELEC.tv · GitHub add lines

Code

sed -e "s,^.*NAutoVTs=.*$,NAutoVTs=6,g" -i $INSTALL/etc/systemd/logind.conf
sed -e "s,^.*ReserveVT=.*$,ReserveVT=6,g" -i $INSTALL/etc/systemd/logind.conf
sed -e "s,^.*KillUserProcesses=.*$,KillUserProcesses=yes,g" -i $INSTALL/etc/systemd/logind.conf

The other option is to just use custom file in projects/YOUR_PROJECT/filesystem/etc/systemd.

it work,thank!