Default [Q] Bulletproof kernel not working properly

Hi,

First of all, I'm quite a noob, so thanks for your consideration.
I just installed the Bulletproof (version 13.0) kernel on my International HTC One, using TWRP Recovery, to disable write protection.
However, write protection is still active, as I can't edit files in the system folder of my phone.
I guess Bulletproof is installed properly, as the 'Sweep2Wake' function is working.

So, my question is: How do I disable this write protection now I'm in a custom kernel?
I am rooted, using Bulletproof kernel and Android Revolution HD 51.0

Thanks in advance,
Sander