You need to add that as a suffix of the dynamic, in the Properties panel.
It’s probably best as an expression using the dynamics popover, unless you want it to trigger a specific key switch, in which case you’d want to make a custom playing technique.
Right --but why? Why can’t I just type in “mf bell-like” in the popover without going into the suffix?
It works, but only half way – it comes out as “mf belllike”. The dash disappears - why?
Seems like a bug.
The dynamics popover is quite flexible, but its ability to recognize specialized instructions is limited, since they’re interpreted in the score as dynamic changes. That’s the intended function of the suffix - enter whatever you like as text-only.
I agree, it would be nice if the functionality of the dynamics popover mirrored that of the tempo popover, automatically detecting and parsing out the text you enter. But it doesn’t, for the time being.
Dorico parses out the hyphen because it thinks you are typing a combined dynamic, e.g. of the form “p-mf”. Obviously it’s a false positive in this case.