You should not be doing what you're suggesting - especially in a corporate environment - as the proper use of Styles is the foundation upon which good documents are designed and managed.

That said, you could create another Style with the same specs as the Heading Styles you want to remove from the navigation pane, then use Find/Replace to change from one to the other.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]