Sbom, in a word to be legal "yes"
Under the various Pigs Records Identification and Movement Orders 2011
7.(1) No person may move a pig off a holding unless it has
(a)an ear tag with the letters UK followed by the herdmark of the holding from which it is being moved; or
(b)a tattoo showing that herdmark (with or without the letters UK);
[there are some exeptions, but you asked about slaughter]
IE it is your holding number that needs to be on the pig.
OK so that's the legal position.
However most abattoirs don't care as long as the number on the paperwork matches the pig - after all that is not their responsibility but yours. If there are no problems with the pig, you'll probably get away with it. However you would need to add their herd number onto your list in E-aml, and this may throw up two holdings with the same number - not sure how e-aml treats this.
However to the previous however abattoirs can as part of their trading conditions limit the legal forms of ID - slapmark, eartag and tattoo being the legal options. Some abattoirs insist on only slapmarks, some will allow slapmark or eartag. Most hate ear tattoo's as you cannot easily identify the pig without a lot of handling. If your tattoo is an ear tattoo, and you decide to go with just the existing ear tattoo then you should check with the abattoir.