is it possible to do a global quarantine of a selection of workbooks by
adding the word 'QUARANTINE' to the same cell in each workbook, without
having to open each workbook one at a time. Hopefully I would be able to
specifiy the size and colour of font also.

i.e. selecting a number of workbooks in a folder then running a macro to do
an update to a particular cell. Or is there a system already built into Excel
to allow this? Ihaven't found one.