Hi Donna, I'm not familiar enough with either frontpage or Expression web to answer this question directly. However maybe these suggestions will help.
A search on "find and replace" suggests the find/replace dialogue allows you to create reasonably complex queries that might do what you want.
Another is not to think in terms of find/replace, but in terms of changing styles, and search around that theme.
There also seems to be lots of sources dedicated to Expression web, as well as a lot designed to help Frontpage users adjust. A search on "changing from frontpage to expression web" brought up a Microsoft tutorial [expression.microsoft.com] that talked about changing styles after selecting text (about 1/2 way down that page) - and it "made sense" to me as a technique suitable for what you want - although it didn't use the search/replace. AS my search term wasn't very well formed, something better worded may lead you to a better source of information.
Not an ideal response, but hopefully gives you ideas that might lead to the answer you need.