https://makemusic.zendesk.com/hc/en-us/community/posts/115007014407-Chords 

As far as I can tell, the line is diagonal, not straight (if that's what you mean!)

The half-dim symbol is in slot 90. You can enter it by Root-colon-90. On a Mac, you can do Root-option-o.

Chord suffixes are document specific (not program specific).

A document’s chord suffixes are shown in the dialog box Chord Suffix Selection.

If the ø suffix is not in the original document, then there are several options:

1) Open a document (or template) that contains the suffix, create a chord symbol with ø, and copy/paste the chord symbol into the original document.

2) Create a new document from a template that contains the suffix, and copy/paste the music from the original document into the new document.

3) Load a chord suffix library (with ø) into the original document.

4) Create in the original document a new suffix with the ø symbol.

I could be wrong here, but I do not think that SongWriter can do neither 3) nor 4).

SongWriter cannot do 3 or 4; Peter is correct.

The symbol is already in the SW Lead sheet template.