(apologies if I am “stepping in”… but seeing as how I was here anyways )…
Insert a Chord event into the Chord Track (it will appear as an “X”)
Double-click on it, to open the Chord Editor.
Activate the button to the left of the words “MIDI Input” (pretty much hidden until you hover over it ), at the bottom-left of the Chord Editor window.
Play your chord .
BUT: you have to play at least three notes, in order for a chord to be recognised.
So… I am now wondering what the original poster is actually asking… do you mean an “open” chord, with just the root and the 5th?.. if so, not possible, I’m afraid (there has to be a 3rd note).
As regards “customizing” chords in Preferences>Event Display>Chords, I’m pretty sure you can’t create chords that aren’t already in Cubase’s library… it is just for the way those chords are displayed.
I create the perfect fifth by copying the melody line in the key editor window - transposing by 7 and with the cursor at the beginning of the part Ctrl+v to paste the original part.
However I am sure you know this and of course is only of relevance if you want to create a fifth or an octave.
You could create a logical preset to do this and assign it a Key Command. Of course this gives you the 5th in the MIDI Part but not on the Chord Track, which is where the OP really wants it.
Ah, yes… It’s not a chord it’s a interval / no 3rd. And yes as a guitar player I really write lots of music which the chord is says E5 or A5 (for example). Even though just two notes isn’t technically a chord, this would work well in Cubase Chord track. If adapted it could make use of Cubase voicing features to add this pleasing and common writing shape to the palette.
I remember a Frank Zappa interview somewhere where he said two-note, fifth “chords” were good because they leave a lot of harmonic possibilities open … or something like that. as you know, writing about music is like something or other.
But yeah, it’s a shame you can’t specify a 5th chord in the chord track. I find the voicing options of the chord track restricting too, and there’s no control of register without adding a transpose insert, right?
Adding the ability to make a “custom” chord voicing that does not have to conform to someones idea of what is musical whether it is technically correct or not would go a long way