Ouch! Don’t practice on your emonTx4. Get a piece of stripboard and a ‘grab bag’ of components, and practice on that. Also buy a solder sucker or desoldering braid and practice desoldering and removing components too. (I’ve never managed to get on with the braid.)
Desoldering plated-through holes – which the emonTx4 has – is VERY tricky and you’re likely to damage it if you try.
If you decide the problem is the connector and you need to replace it, I wouldn’t even try to desolder a 9-way connector in one piece, it would be much safer to destroy the moulded housing in situ without touching the pcb, and then remove the remnants of the individual sockets one by one.
If the calibration numbers match the c.t’s you’re using for the respective inputs, then you should be close enough for most purposes. You can fine-tweak the numbers if you need to.