How to make "Maximum quantity per order" 1 for all

Hi, my site is only for digital goods (downloadable product)
I would like to have a global option to set Maximum quantity per order -1
then i will not need to add it on every products

Please, if any core code modification change needed would be great so.

You can do that with a mass action:
www.hikashop.com/support/documentation/167-massaction-form.html
No code modification needed.