Changing attributes of text box manually added using plot editor

After plotting a data set and adding text box annotations using the plot editor, I would like to run a script to set some of the attributes in all of the text boxes I have added manually.

I have been trying to use the find object command, but it is not working.

Tbox = findobj(gcf, 'type', 'textbox')

set(Tbox, 'Margin', 200)

Any suggestions would be much appreciated!

Thank you,

Chris