One way :

Sub ModifyComment()
Dim strS
strS = ActiveCell.Comment.Text
ActiveCell.ClearComments
ActiveCell.AddComment Text:=strS & "Your addition to comment."
End Sub

HTH
Paul
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Be advised to back up your WorkBook before attempting to make changes.
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Hello!

If I have a cell with a comment in it, what code would I use to add
more comments to the current comments? The comments I will be added
will be hard coded, nothing that the user would enter.

I am using the .offset command for the appropriate cell.

Thank you very much in advance,
E2L