Install mongos as a service using mongos.exe --install --logpath<> --configdb <>
Now create a config file mongos.conf
configdb = localhost:30000
logpath = c:\data\mongos.log
serviceDisplayName = Modified Service Name
serviceDescription = Modified Service Description

try to reinstall service with mongos.exe --reinstall --config mongos.conf

This fails with

Tue Jul 10 23:50:31 warning: running with 1 config server should be done only for testing purposes and is not recommended for production
Tue Jul 10 23:50:31 Trying to remove Windows service 'MongoS'
Tue Jul 10 23:50:31 Service 'MongoS' removed
Tue Jul 10 23:50:31 Trying to install Windows service 'MongoS'
Tue Jul 10 23:50:31 Error creating service: The name is already in use as either a service name or a service display name. (1078)