The information will be retained - the CSS code in your StyleSheet will
simply hide it (prevent it from being rendered). So you can always go
back if you like.
> I imported a tiddler with a script to hide the subtitle but nothing
> happened after I saved and reloaded the page.
You don't need to import this like a plugin; simply add the code to your
StyleSheet (accessible via the sidebar tabs' More > Shadowed menu):
.tiddler .subtitle {
display: none;
}
HTH.
-- F.