Use start up command line to change file location

Question

I am currenlty using a .bat file to start Blender, with this

set PYTHONPATH=
"%~dp0\blender" 

So that I can use the local Python folder.

Is there a way to tell Blender to look for a file in a different location?

For example of I wanted to setup a default start file to be on the D:\custom location rather than C:\Users\USERNAME\AppData\Roaming\Blender Foundation\Blender\3.1\config