In order to simulate in TCSH the effect of 'source activate $env_name' (which only works in BASH), it is necessary to both re-set the PATH environment variable *AND* to set the CONDA_DEFAULT_ENV environment variable.

Added 'setenv CONDA_DEFAULT_ENV $env_name' to the content appended to ~/.cshrc

This MIGHT even be the last thing necessary for this to work. Have already had some success updating some packages in the new environment!