I would like to share how to set the UnitSystem to the SI by default. To open the file, evaluate:
SystemOpen[FileNameJoin[{$UserBaseDirectory, "Kernel", "init.m"}]]
Then add this code:
$UnitSystem="Metric";
Then run the code and save the file. Then do the same for the file at
SystemOpen[FileNameJoin[{$BaseDirectory, "Kernel", "init.m"}]]
I have tried figuring out how to programmatically edit the init.m notebooks with like NotebookWrite or NotebookPut but I haven't figured it out so far. If anyone else knows how I could make this into a program that could be run in one iteration please comment.