The TNG RFID Tag or sticker cannot be shared between several vehicles and if you're caught doing so, there's the risk of your tag getting suspended.
Portable device for RFID stickers for sale?
You've seen these plastic things with suction cups that have been used to mount the vehicle's road tax sticker on the windshield? Apparently, you can now get a smaller version of it on multiple e-commerce platforms specifically designed for the TNG RFID tag.
This means that it can be easily removed and placed in different vehicles, but that doesn't mean that it is okay to share. Why? All toll booths with RFID lanes are equipped with Automatic Licence Plate Recognition (ANPR) which can detect any mismatch between the RFID tag or sticker and the vehicle's license plate.
RFID tags should only be used with the vehicle it's registered to
This is actually clear as day on the Touch 'n Go's Frequently Asked Questions (FAQ) page and if you're caught with this violation, it may result in the suspension of the RFID tags or stickers.
So, just follow all the rules and regulations by sticking it properly on the front headlight or windshield to avoid this from happening. Trust me, you don't want to be the person causing an unnecessary jam in the RFID lane, especially during rush hour. Not fun.