Explicitly modifying a style in the Modify Style dialog box will often be better, in the sense that you get full control over the modifications made.

However, the Update <style name> to Match Selection command should be predictable. The command would only add content that was added as overrides (direct formatting) to the underlying style. This applies to both paragraph and character styles.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional