Managed to relink the chain this evening without much difficulty, having had the tricks demonstrated to me¹. It's not ideal having it shortened, so will go for complete drive system replacement next week. The chain and cassette are sufficiently old that they'll have worn together making a new chain unusable on the existing cogs, and the chain wheel is a bit bent anyway.
Anyway, the patched up chain was good enough to get me round to vyvyan and razornet's place for dinner and Battlestar Galactica (the new version), and back again without any signs of further problems.
¹ Don't take the pin all the way out, just far enough to separate the links, which makes putting it back together much easier. Flex the chain laterally (i.e. not the way it naturally bends) after relinking to ease the new link and make it rotate freely, this really did work wonders.