From the manpage:
A login shell begins by executing commands from the system files /etc/csh.cshrc and /etc/csh.login. It then executes commands from files in the user's home directory: first ~/.tcshrc (+) or, if ~/.tcshrc is not found, ~/.cshrc, then ~/.history (or the value of the histfile shell variable), then ~/.login, and finally ~/.cshdirs (or the value of the dirsfile shell variable) (+). The shell may read /etc/csh.login before instead of after /etc/csh.cshrc, and ~/.login before instead of after ~/.tcshrc or ~/.cshrc and ~/.history, if so compiled; see the version shell variable. (+)
There is no argument of environment variable to change this, except for -f to prevent loading a startup file.
You can use the source command to load a file from within tcsh, though:
source /etc/my-special-settings.tcsh You could also do something like this in your user's ~/.tcshrc:
if ( $?SPECIAL_SETTINGS ) then source /etc/my-special-settings.tcsh else source ~/.tcsh/tcshrc endif