Something like this?
Option Explicit
Sub AppendToExistingOnLeft1()
Dim c As Range, mR As Range, txt As String, yn As String
Set mR = Application.InputBox("Select your Text", , , , , , , 8)
If mR Is Nothing Then MsgBox "Nothing Selected!", vbExclamation: Exit Sub
On Error GoTo 0
txt = InputBox("Please enter the text you want to add...", "Enter text...")
yn = MsgBox("Add this text to the beginning? (If no, it will be added to the end!)", vbYesNo, "Where to add text...")
For Each c In mR
If yn = vbYes Then
If c.Value <> "" Then c.Value = txt & " " & c.Value
Else
If c.Value <> "" Then c.Value = c.Value & " " & txt
End If
Next
End Sub