To merge formats, use the [StyleReplacements] section to map each format to an existing RTF style. For example:
[StyleReplacements] ; Document para format name = replacement existing RTF style name ; the RTF name need not be unique, and may be created in [Styles] ; the properties of the original style remain as-is in the text ; unless Template and TemplateAutoUpdate are set in [WordOptions] HeadingRunIn=Heading 2 SubHead=Heading 2
DITA2Go ignores any assignment in the [StyleReplacements] section that has no entry to the right of the equals sign.