Since macOS Sierra this is no longer normally possible, though you can alter. Bootcamp to reinclude this option.
Alternatively, you can create a bootable USB using the terminal, or using an application like UNetbottin. You can find instructions for how to use the UNetbottin, and for using the terminal or reincluding the option in Bootcamp.Note, altering the package contents of Bootcamp also no longer seems possible in macOS Sierra. At the moment, I do not know of a method to change/overwrite this. Hey guys I know this is an old topic but in case someone still looking for the solution. I found a way to edit the Boot camp assistant info.plist You cannot alter info.plist if you are booted from the same hard drive. You'll need a second partition with MacOS X installed.
In my case I have two partition with High Siarra installed on both partition. And boot from the one you don't want to alter. In my case my second HDD. Now just open finder and navigate to the HDD you want to alter and just copy info.plist to Desktop and make a backup of it before you edit. Now you can follow Note: I try to edit with OS X default TextEdit but it doesn't work and I use sublime text, then it works fine.
When the USB drive is ready you can plug it in you mac and press alt (option) while booting, you have inserted a firmware password, it will ask you to unlock the firmware by inserting that password, else it will take you to all the bootable drives, including your USB device.
This can be done by console. First start connecting your usb drive and type diskutil list to display all connected drives.