I can change the continuation line on a rallentando to solid, dashed, or dotted; but I don’t want a continuation line to show at all. How do I do that?
Also, after selecting the rallentando marking, have a look in the Properties panel under Tempo. Click on Gradual style and set it to rit. . The other choices are rit… and rit - ar - dan - do .
There is also a property for Line style (Solid, Dotted or Dashed).
The page in the manual for that property is here, for your reference.