Phone [Q] Xperia SP 4.3.3 Root Keeping DRM Keys

I have an Xperia SP currently running 4.1.2 rooted, bootloader locked.
My aim is to upgrade to 4.3.3 and root, for which i will have to unlock the bootloader. To do so I need a TA partition, for which again, root is required.
So, my question is that is it okay if I take a TA Backup now [in 4.1.2] and then upgrade OTA and unlock bootloader, root and then restore the 4.1.2 TA backup onto 4.3.3 in order to restore DRM keys and Relock the bootloader?
Has anyone done this?
is it safe?