Change the text of a selected item in a combobox

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VB

Hi everyone.

This is a bit of an unusual problem.

I have a ComboBox (with DropdownStyle = DropDown)
The user can either type something in the ComboBox or select an item from the drop down list.
If they select a specific item ie "Painting as per Quotation ......." I would like to change the selected item to say "Painting as per Quotation Q2020-001". The Quotation Number is retrieved from another ComboBox.

The code that I'm using (see below) does not change anything - the Combobox remains unchanged.

Could anyone advise if this is even possible and how I could achieve my desired result.

Many Thanks

What I have tried:

Private Sub cbo_Desc_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cbo_Desc.SelectedIndexChanged,
       Dim NewText As String = ""

       If cbo_Desc.Text = "Painting as per Quotation ......." Then
           NewText = cbo_Desc.Text.Replace(".......", cbo_Quotation_Number.Text)
           cbo_Desc.Text = NewText
       End If

 End Sub