For example, I need to switch Cygwin sshd service from 'ntsec' to 'nontsec' mode on quite a few Windows machines without re-installing the service.
The variables are stored under
registry key. So, the following commands do the trick for sshd example:
regtool set /HKLM/SYSTEM/CurrentControlSet/Services/sshd/Parameters/Environment/CYGWIN nontsec # don't run the following commands one-by-one unless you want to lose remote access cygrunsrv -E sshd && cygrunsrv -S sshd