Please put the files into the right place when installing.
But for “editing” systemd-units installed by a package I really suggest using “systemctl edit $unit”
which will create a drop-in.
When the maintainers add new stuff in their unit-file which are necessary for something and you just copied over the original file and edit it, the chances are higher that it breaks with future updates.
Only put completely new stuff into /etc/systemd/system that you created.