As far as I understand psychosurgery requires simulspace and the acceleration to boot. The procedure goes as follows: 1.You load the EGO. Because every transhuman ego is a neural network, which is basiacally a weighted graph (altough with 86 billion nodes). 2.You analyze the graph with software. 3.Then you make changes to the graph/ego. Many sets of changes. 4.You run every modified ego in simulspace, testing them and evaluating effects of the changes. 5.You cherry pick the best modified egos. 6.If you're satisfied with the effects, you end the procedure if not repeat the steps. As you can see the acceleration is almost mandatory. Psychotorture works the same way. You fork the poor soul and then torture every fork individually to see what works, throwing in ego modifications along the way. So psychosurgery is pretty terifying in itself on the count that you create dozens to thousands of forks and then delete them. Exhumans are only slightly more barbaric. Every merging goes along the same lines. You bash together two fork egos until something stable goes out. Because the egos being bashed together are really similiar the procedure is mcuh faster and can be somewhat automated, but its basic principle is the same as normal psychosurgery. It is one of the reasons why forking is not universally endorsed practice. Only most utilitarian and "self-ruthless" personalities can utilise it to full extent. After all EP is a horror game. It is only made worse by the fact that this future is so realistic (some aspects ego manipulation amongst them) So the mechanical penalty may be beacuse as the surgeon accelerates, they have less subjective time to test the changes. For a one week procedure if they work in 1xtime their patients/victims have 60 weeks of testing. When surgeon accelerates to 2x and the whole realtime shortens to half a week the patients got only 30 weeks of testing. I won't fully flesh out the logic hoping that you can follow it yourself. I myself would say that the -20 penalty is for purely mechanical reasons and above explanation is rationalization. MULTIPLE EDITS ABOVE.

You don't need to make forks to do psychosurgery though, it can be done with a single ego on hand. I think it's basically a case of applying patches, observing what happens, and removing them quickly if they don't work. Acceleration would make that harder as your margins for safe removal would narrow. Messing with a brain's I/O system is still fairly brutal without disposable forking though.