This is like this historically, since Centre/SIS.
I have checked openSIS, they still do like that (the Rollover program rewrites the
config.inc.php file with the new school year): https://github.com/OS4ED/openSIS-Classic/search?q=%24DefaultSyear
I have tried, a long time ago, to move it to DB (as having the school year inside the config.inc.php file obviously adds friction), but as I remember, I had faced some errors and behavior I was not able to fix.
That being said, the modification is quite easy to achieve. Please see by yourself and if you achieve something usable, please share it