Update vba code through user input.

I think I am just hoping for an easy way out but is it possible to have self updating code based on user input?

I have a form that includes a combo box. As an example lets say I had this...

Sub frm_Mode_Initialize()
    'Clear previous values.
    frm_Mode.cmbBox.Clear
    With frm_Mode.cmbBox
        .AddItem "blue"
        .AddItem "red"
        .AddItem "yellow"
    End With
    frm_Mode.Show
End Sub

where frm_Mode would allow the user to pick blue, red, yellow, or enter a new value. If the user entered a new value could I add add this to the initialize list for future use? OR will I have to keep track of this in a hidden spreadsheet or something similar?

TL:DR -> I am pretty sure I am expected to much out of VBA but it would be reassuring to know self updating code existed.