I've tried using xcacls and cacls on a Windows Server 2003 computer but they all replace the existing permissions when I use /g. Does anyone know of a command-line tool that will simply add permissions?
Make sure that you use /G and /E (edit mode) together (and most likely /T as well).
For reference, here is the complete usage information from the command
CACLS filename [/T] [/E] [/C] [/G user:perm] [/R user [...]] [/P user:perm [...]] [/D user [...]] filename Displays ACLs. /T Changes ACLs of specified files in the current directory and all subdirectories. /E Edit ACL instead of replacing it. /C Continue on access denied errors. /G user:perm Grant specified user access rights. Perm can be: R Read W Write C Change (write) F Full control /R user Revoke specified user's access rights (only valid with /E). /P user:perm Replace specified user's access rights. Perm can be: N None R Read W Write C Change (write) F Full control /D user Deny specified user access. Wildcards can be used to specify more that one file in a command. You can specify more than one user in a command. Abbreviations: CI - Container Inherit. The ACE will be inherited by directories. OI - Object Inherit. The ACE will be inherited by files. IO - Inherit Only. The ACE does not apply to the current file/directory.