Find and replace multiple lines/paragraphs

Testing here, it seems that the VBA Replace() command is not subject to a character limit.  Therefore, you can use:

Dim strFind As String

Dim strReplace As String

strFind = ""

strReplace = ""

With ActiveDocument.Range

    .Text = Replace(.Text, strFind, strReplace)

End With

where you copy and paste the text to be found into the strFind = "" and the replacement text into the strReplace = "" such as:

Dim strFind As String

Dim strReplace As String

strFind = "On the Insert tab, the galleries include items that are designed to coordinate with the overall look of your document. You can use these galleries to insert tables, headers, footers, lists, cover pages, and other document building blocks. When you create pictures, charts, or diagrams, they also coordinate with your current document look. You can easily change the formatting of selected text in the document text by choosing a look for the selected text from the Quick Styles gallery on the Home tab. You can also format text directly by using the other controls on the Home tab. Most controls offer a choice of using the look from the current theme or using a format that you specify directly."

strReplace = "Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Maecenas porttitor congue massa. Fusce posuere, magna sed pulvinar ultricies, purus lectus malesuada libero, sit amet commodo magna eros quis urna. Nunc viverra imperdiet enim. Fusce est. Vivamus a tellus. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Proin pharetra nonummy pede. Mauris et orci."

With ActiveDocument.Range

    .Text = Replace(.Text, strFind, strReplace)

End With