Yes, they have
to get disassembled. A lot of people have asked that, actually... is there a particular reason it gets asked?
I'm not sure it's quite understood what is involved in disassembling a turbo for this purpose. The cartridge is left completely untouched. The housings simply slide off of the cartridge and it's EXTREMELY simple to do. It's not a delicate or complicated procedure and doesn't involve special tools or anything. There's one 10mm nut that holds a v-band clamp on the exhaust housing.... loosen that and the housing literally just pops off. The compressor side is different on a lot of turbos but it's either like 6 small little bolts that hold it on (take the bolts off and the housing just slides off) or it's a large snap ring. The important part, the cartridge, doesn't get tampered with in any way
...and on top of the simplicity with which the housings come off, all of the OEM Subaru turbo housings have a mark or a 'pin' (and a hole on the cartridge) on them so they line up perfectly when they're reinstalled. On turbos like Garrets, we make an indexing mark or use a reference on the turbo to make sure they line up properly when assembled.
Make sense? The hard part is in porting properly
so efficiency is truly increased, not reduced.