I would approach this task from a different direction.
Firstly, if you have control of the receiving file PRIOR to introducing the other content, add a couple of aliases to the heading styles so that the conversion of Epic Title and Main Topic to headings happens automatically as you paste.
Add an alias to Heading 3 by modifying the style for Heading 3 so its name is "Heading 3,Epic Title". Do the same for Heading 1 so its name becomes "Heading 1,Main Topic".
Note: You can't add an alias if that style name already exists in the document so it has to happen BEFORE pasting in the content from the other source. But once it is done, anything that was styled with either Heading 3 OR Epic Title will paste into the document as Heading 3.
So then, all that remains is the question you posted about. I would rewrite that part of the macro along the following lines.
Code:
Sub ChangeActiveDocument()
Dim aRng As Range, iHeadStyleID As Integer
For iHeadStyleID = -4 To -2 '-4=wdStyleHeading3, -2=wdStyleHeading1
Set aRng = ActiveDocument.Range
With aRng.Find
.ClearFormatting
.Style = iHeadStyleID
.Wrap = wdFindStop
.Forward = True
.Text = ""
Do While .Execute
aRng.ParagraphFormat.Reset
aRng.Font.Reset
Loop
End With
Next
End Sub