The Find/Replace expressions in my previous post were for changing exiting periods to not underlined. To add periods to Heading 2 paragraphs that don't already have them, use a wildcard Find/Replace, where:
Find = ([!.])(^13)
Replace = \1.\2
and specify the Heading 2 Style. After that, do the standard Find/Replace from my previous post, retaining the Heading 2 Style and specifying the replacement as not underlined.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]