Personally I hate it when people put metal tags on weaners! What chance have their ears got to grow without them digging in? The plastic ones are much kinder and don't get caught up in anything.
Now the weaners are with you and not moving anywhere until they go to the abattoir then don't worry. You will need to identify them as yours to go to the abattoir anyway...In this area that has to be a metal tag with your name on. In other areas it can be a slap mark, plastic tag or metal tag.
I have GOS here, and I identify all piglets with plastic tags. Then if they are destined for meat they get their metal tag while they are eating the evening before they go off.
Enjoy your pigs, they are wonderful!!!