When configuring a MSREGWR, using a named register (single 16 bit unsigned register) and function code 16, setting the Local Address to a constant (16 in my case) results in a green dot, but clicking save gives the error message that the Local Address cannot be a constant. Setting the function code to Write Single Register gives the expected red dot.
Also, consider having the range info notes from the device profile register entry show up somewhere on the MSREGWR item editor window.