Hi Pamenifor,
It is not possible to edit a number of boundaries at the same time.
I'm not sure whether you use constant values or time series (external files) to define the flow values, but in case you use external time series, and if you simply need to change the name of the time series for each boundary, you may change this by editing the *.bnd11 file in a text editor (like NotePad), in which you can use the "Search and replace" option to search for the name of the previous time series and change it to the new one.
Hope this information may help.
Best regards,
Mathieu