I think to disable SIP you are supposed to do it in terminal from the recovery partition.
The post in apple's developer forums you linked to says:
/usr/bin/csrutil disable - Turns SIP off of the boot drive. Must be run from Recovery with a reboot to take effect.
Yes, you do have to boot into the Recovery HD to accomplish this. My problem is the security command was not available in my Recovery HD no matter what I tried. So this was the solution (not created by me) that worked for me to disable SIP:
- Boot into the Recovery HD (holding Command-R after the chime and until the progress bar appears)
- Launch Terminal from the Utilities Menu.
- Enter /usr/bin/csrutil disable and let it do it's work. It took maybe a minute for me.
- Reboot back into your regular El Capitan installation and SIP is off.