I've finally realised the 170mm travel on my Lyriks is far too much for most of the riding I do in the Peak. I'd like to change to 150mm, but keep the parts so I can swap back to 170 if I ever make it back to BPW or the Alps.
For fork is a Lyrik RCT3 bought in early 2019 - so perhaps a 2018 model. Am I right in thinking this is the bit I need? If anyone has one they're looking to shift, please let me know. I've heard it's a relatively easy job - any tips from those who've done it will be gratefully received!
Thanks!
Or this one? 
Plug the serial number into the Rockshox trail head app to confirm.
There's also the B1 air shaft, which gave a bigger negative air chamber and was much plusher than the A1.
Having now tried the C1 as well, I prefer it to the B1. I love how it holds the front up so well, while still being very supple - but I know others have been less impressed.
Fitted a longer C1 shaft to mine last week. Very easy, if you do your own lover service then you can do this. If you are going to swap back, I’d buy the complete air spring as it saves swapping the bottom pieces each time. Only £45ish for complete assembly.
B1 shaft was very plush, too much for my liking. It sagged a lot under bikes weight.
C1 still plush but rides higher in travel which I prefer.
Like other said check code on fork to see what you have already.
That looks right, but I'd get the full assembly, as opposed to just the shaft if you plan to swap over and back. Will save a lot of hassle.
If your fork doesnt say debonair at the top of the air spring stanchion its probably the first debonair without the red bits, if it does you'll have a B1 in there, Biketart had the best uk price C1 £37.80 but currently out of stock, send them an email to see if they're coming in soon.
Thanks all, that's helpful. I'll grab the serial number to double check. I think the fork does say Debonair on it somewhere...