Yes on both counts... You can upgrade TWRP anytime, it is not an issue and the latest works fine. SuperSU update should be fine, you will update the app first through the play store, then update the binary in the app, it will install the binary in the same manner as SuperSU is installed currently.I followed these instructions many moons ago, and it has worked great ever since. However, I just received an update notice from the Play Store for SuperSU 2.76 (Released today). Am I reading an early post correctly that it is safe to upgrade as long as the SuperSU specified in the OP was used during the initial install? As always, I have made a TWRP backup just in case. Can I update TWRP as well (To 3.0.2-r1)? I just like more or less keeping up with any bug fixes / security updates, or is this a matter of "If it works, don't fix it".
I am currently at:
If you are really worried about it, download the latest ZIP here: https://download.chainfire.eu/supersu/ then in your phone go into SuperSU and do a complete unroot, reboot to verify root is gone, and flash the latest ZIP using the manual systemless method.