Hello Eoin and welcome to GoY. I don't grow Cordyline's myself, but I think it's a bit early in the year and rather cold to prune this plant yet. I'd do what you describe in the spring as being pruned tends to provoke plants into growing and I think there's quite a bit of cold weather yet to come before this winter's over. If you prune now those new shoots stand more chance of being frost nipped.