A family of Microsoft word processing software products for creating web, email, and print documents.
There are a couple of ways to do that.
Since Word automatically applies the Footnote Text style to footnotes as they're created, you can limit the Find/Replace to text having that style (assuming you haven't changed the style of any footnotes). In the Find/Replace dialog, click the More button to expand the box. Click in the Find What box, click the Format button at the bottom left, click Style, and select Footnote Text in the style list. Set up the rest of the Find What/Replace With entries as needed, and click the Find Next or Replace All button.
If you're doing this in a macro, it's even easier. Declare a Range variable and set it equal to ActiveDocument.StoryRanges(wdFootnotesStory); use the Find method of that range to do the replacements.
Dim rg As Range
Set rg = ActiveDocument.StoryRanges(wdFootnotesStory)
With rg.Find
.Text = "find this"
.Replacement.Text = "replace with this"
.Execute Replace:=wdReplaceAll
End With