adb build.prop restore - rooted phone but cannot gain SU or 'root' in adb.

Hi all,

I have been through douzens of threads and forums looking for a solution to this.

I followed some instructions to modify the build.prop file on my Huawei G535-L11 to disable Huawei theme manager in order to get Xsposed working fully (changed ro.config.hwtheme: 0). I did a backup of my original build.prop before hand, and my phone was rooted and unlocked but running the stock rom.

Unfortunately, it rebooted but won't go past the first 'EE' splash screen (just turns off again).
I can inconsistently get in to both fastboot and Android recovery, so I have been trying to use adb to push the original build.prop to /system/ on the phone.
However, this fails as /system/ is apparently RO. I have now discovered that I can't get SU permissions despite my phone being rooted.
If I try:
adb shell
$ su
nothing happens and it goes back to a $ prompt.
If I try:
adb root
I get the message (paraphrased):
adb cannot run as root in production builds.

So I can't push or do any adb method of restoring the build.prop file?! I don't understand why it is acting as if it is not rooted. I had Link2sd, Gravity Box, No Frills Cpu Controller all set up and working before, so I'm fairly sure I did truly have root.

I have also tried flashing a TWRP recovery, which apparently is successful, but when I go in to recovery it is still the Android Recovery.

Does anyone have any ideas what I could do to get my phone working again please?! This is my last gasp before the phone gets filed under 'B' in the cylindrical cabinet in the corner of the room!

Any assistance greatly appreciated!