ListBox Existing Value Or User Choice

I have a form users can use to input information into a spreadsheet, but also use to recall data (so they can search for a record, recall it, amend one or two fields and then re-save it)

I would like a listbox to display what is already in the cell in the worksheet to start with. Only when they then click in the listbox would they then get a list of predefined options.

So they recall the data onto the from and the listbox says "squatters", because it is an old value that shouldn't be used anymore. Once they click to choose another option, however, they only get a choice of either "vacant", "occupied" or "WIP" (for example).