If they have 2, and they are going for slaughter under a year old anyway you don't need to do anything with the tags. Thats their own numbers, full stop.
Copied from Defra website -
Identifiers for lambs and kids intended for slaughter
If you intend to slaughter a lamb or kid (ie a sheep or goat that’s less than 12 months old), you can identify the animal with a single ear tag, instead of 2 identifiers.
The single ear tag only displays your flock or herd mark. It doesn’t display an individual identity number for the animal.
Slaughter ear tags are labelled in the 8 character format, UK 123456, where 123456 is the animal’s 6-digit flock or herd mark.
From the start of 2015, the single ear tag on slaughter lambs will be a yellow EID that contains an individual identification number which can be electronically scanned. The individual identification number won’t be displayed on the EID tag.
You can continue to use a single conventional (non-EID) ear tag for slaughter kids after 2015.
If you decide to keep a lamb or kid that’s identified by a single slaughter tag beyond a year old, you must replace it’s single tag with a pair of identifiers before its first birthday.
If the lamb or kid is no longer on the holding where it was born, you can only do this if you can individually trace the animal back to its holding of birth.
actually just realised it says 'kids' not lambs, so are yours eid tags?
'If the lamb or kid is no longer on the holding where it was born, you can only do this if you can individually trace the animal back to its holding of birth'.
why can't you just get red? replacement tags if you can't trace to birth holding?