Okay, I know what I want to alter, but I can't figure out how to do it with WHM's "advanced" exim config editor, which has to be the most cockeyed configuration editor I've ever seen.

In the uneditable section titled Main Configuration Settings, we find this:

# The use of your host as a mail relay by any host, including the local host
# calling its own SMTP port, is locked out by default. If you want to permit
# relaying from the local host, you should set
#
# host_accept_relay = localhost

In most config editors, I would just remove the # to enable that setting, then I would get on with my day. Not so with this thing. If I try entering that line, without the #, in the very next editable area, the processing page tells me there's a syntax error, and I have to go undo it. So how, practically speaking, does one go about activating a commented-out setting in the exim config editor?