No abattoirs can accept a temporary mark anymore, rules changed last year for scotland.
The tag only needs your herdmark on it, there is no individual ID required for pigs.
If the pigs came to you with a tag, then legally you should re-tag (leaving the old one in) with your herdmark when they go to slaughter. However since no-one checks that the herdmark matches the sending holding, this is largely ignored, and having more than one tag just adds confusion at the abattoir.
As long as the number of pigs on your holding matches the net of your on and off moves, Defra will be happy, and once killed of course there is nothing to match paperwork against !