Rockshox steerers are definitely press fitted. The longest uncut steerer tube lengths I have found seem to be 265mm - this appears to be a standard across quite a few manufacturers. It's really unfortunate that they made a head tube so long - very unusual.
To replace a steerer on a Rockshox fork you need to purchase a whole new CSU - none of them are screwed or clamped in. It's cheaper to buy the whole CSU from Canada on eBay including the carriage charge (they are almost half the price compared to buying them in the UK).
If you are getting a new fork, I recommend getting a fork at the standard 265mm steerer tube length and then using a riser bar with your stem to preserve your current handling set up. From the looks of it your stem looks like it has a height of 40mm and assuming your max steerer tube length is 265mm then you'll be 25mm too low. Therefore, you need a riser bar with about 30mm rise. I guess you may know already, but if not, Chain Reaction is a good place to buy bits like this.
Here is one with 30mm rise and a bargain at the moment.
Crank Brothers Iodine 1 AM Riser Handlebar | Chain Reaction Cycles
This bar fits into a 31.8mm stem bar clamp. Check your stem bar clamp internal diameter to make sure the bar will fit.
Crank Brothers Iodine 1 AM Riser Handlebar | Chain Reaction Cycles
To replace a steerer on a Rockshox fork you need to purchase a whole new CSU - none of them are screwed or clamped in. It's cheaper to buy the whole CSU from Canada on eBay including the carriage charge (they are almost half the price compared to buying them in the UK).
If you are getting a new fork, I recommend getting a fork at the standard 265mm steerer tube length and then using a riser bar with your stem to preserve your current handling set up. From the looks of it your stem looks like it has a height of 40mm and assuming your max steerer tube length is 265mm then you'll be 25mm too low. Therefore, you need a riser bar with about 30mm rise. I guess you may know already, but if not, Chain Reaction is a good place to buy bits like this.
Here is one with 30mm rise and a bargain at the moment.
Crank Brothers Iodine 1 AM Riser Handlebar | Chain Reaction Cycles
This bar fits into a 31.8mm stem bar clamp. Check your stem bar clamp internal diameter to make sure the bar will fit.
Crank Brothers Iodine 1 AM Riser Handlebar | Chain Reaction Cycles