Interesting point "A circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except a
lampholder having no exposed-conductive-parts and suspended from such a point." do not stipulate what voltage. However, clearly can't have an earth if SELV. I would just tape it up, and you never know when you will want to return to 230 volts.
Technically, we no longer have MR16 the MR stands for multifaceted reflector, and modern LED lamps don't have a reflector, and when we did have reflectors both GU10 bases and G5.3 bases were both MR16, the main difference was with G5.3 we normally use a circlip to retain the bulb, but the GU10 uses the base to retain the bulb, so G5.3 to GU10 easy, but the reverse how do you hold the bulb in place?