Hey I was just thinking about this the other day not particularly for the failing cat but for a small increase in bhp did a bit of looking around. Yes basically, u will have to remap again after installation. If you alter/ change any flows of any substance to the engine a remap is required to maximise efficiency and engine longevity.
Do you know the inside diameter of the sti pipe? As I'm mindful that you have to get right the kind of flow. Other forums have suggested the 3'' pipe would make turbo sluggish from less pressure against a smaller diameter pipe.
Where would you get a sti pipe?
I've seen a japspeed pipe 75 pound ish
I'm thinking flexing pipe in the middle would be less stressful on engine as it jumps around under the bonet. Standard, I think its a solid one.