That is mostly how you should update it. You will need to replace the rs code for the instance with the variable and end the if a little earlier like this:
<%
Dim theVal = rsPropertyTable.Fields.Item("Content").Value
If IsNull(theVal) Then
theVal = ""
End If
' WebAssist iRite: Rich Text Editor for Dreamweaver
Dim WARichTextEditor_1 : Set WARichTextEditor_1 = CreateRichTextEditor ("Content", "../WA_iRite/", "800px", "800px", "Custom", "../custom/property-update_Content2.js", "" & cStr((theVal)) & "")
%>