Changing / adding environment variables
From WPKG | Open Source Software Deployment and Distribution
Windows variables are stored in the registry. You can change them by adding or modifying values in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment.
Below, an example for adding two variables for Cygwin - with it, applications using cygwin1.dll will be able to use UTF-8 characters in file and path names:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment]
"CYGWIN"="codepage:utf8"
"LC_CTYPE"="C-UTF-8"
Import with:
regedit /s "%SOFTWARE%\cygwin.reg
Windows 7 comes with the command "setx" which can change environment variables in several ways.