I would like to notate a four-part chord containing three adjacent chromatic pitches and switch off the split stem for the full chord. A two-part chromatic cluster is possible using the instructions here:
but when further pitches are added to the chord it breaks out into a split stem chord. How to switch this behaviour off?
Does the tip at the bottom of that page, about how to change the default setting equivalent of this local one, help in your case?
No, it doesn’t. When the chord consists of just [C, C#] it’s fine but when I add a B or D, the C# splits off to the right.
I’m not sure what you’re after here: if you want to see, for example, the three notes B, C and C# together on a stem, the noteheads would have to overlap, which breaks traditional (and modern) engraving rules. So the split stem is your only option here, if the three notes can’t be respelled or placed on more than one stem.
Hope that’s helpful.