Dear Cesar,
there is no need to edit letsencrpt.tcl. The script creates its own account and manages it. One machine can use many letsencrypt accounts in parallel. It is actually a good idea to use one letsencrypt account for one naviserver to ease moving installations around.
Once the certificate is retrieved from letsencrypt, it is named after the first domain name (e.g. on openacs.org "openacs.org.pem") and inserted in the configuraton file in the "ns/module/nsssl" section, if it is not there already.
Hope this helps.
