The built in aliases could be displayed in a grey color, as opposed to the black custom aliases. Or, even better, they would be grouped
into built-in aliases at the top & custom made ones below.
They are greyed in Prefs. 
Yes, you're right, but i mean the way, they are displayed after typing "/", where they all appear in a black font.
It would make it a bit easier to find the built-in aliases.
FWIW - I think this is useful as well - but I'd actually rather that the built-in aliases were ~grouped separately from the user defined aliases...
Yes, i think that would be much better, to have the built-in aliases in one group, instead of having them scattered over the whole list.
It also would be good, like we have in the tag editor (i think, that was changed some time ago 
), if Opus would remember, if a group is collapsed or not.