This is the procedure I follow when I modify critical files.
1) keep a backup copy using some naming scheme when no version control is available. In this case, for example, I would use initially:
cp .tcshrc old.1.tcshrc
make some changes, then for the next set of changes:
cp .tcshrc old.2.tcshrc
and so on. Once you are satisfied with your changes, perhaps after a few days of successful use, then get rid of the old.n.tcshrc files.
2) always stay logged in 1 session, and test logging in from another session, from another window, computer, or whatever resource you need. That allows you to quickly test your changes, and fix problems or restore from old.n files as needed.
In the current situation, we could only guess as to what the problem is because we don't know what the original situation was nor what the current situation is.
If you can get a command-line login, you can try to restore the .tcshrc file to its original state.
If there is a way to get a default .tcshrc, you might try that. Failing that, you may need to ask the system administrator to do it.
Best wishes ... cheers, makyo