I have a multisite instance of WordPress with almost 100 sites. I need to set an option for a network-wide installed plugin but I don't want to go to each site dashboard to set this option by hand. How could I do ?

The option I want to change is a classic option, not a network-wide one. It comes from a plugin that I did not write. Want I need it to change the value of that classic option for all sites in my network at once.