Thanks @magnusbaeck, much appreciated advice.
I also got some advice from @andrewkroh in the other topic here:
Thanks very much @andrewkroh, I'm going to investigate the possibility of reindexing, and if it proves too complicated/time-consuming/scary I may go with the original 'delete and create' solution (I'll chalk this one up to experience and better planning next time).
Thanks to you both for your help.