I believe Rand using the true power was a surprise to the shadow. They will however see it as an unexpected boon and try to use it to give them an edge. It will even seem to work. But I have a feeling in the end the true power will be the means to victory by Rand.

As far as Semirhage torturing Rand, I mean, how could she resist? She is who she is. It is possible the DO or Moridin were willing to sacrifice Semirhage -- the DO or Moridin probably knew Rand would escape somehow -- the Pattern will do all it can to to make sure Rand reaches the last battle. So the command to not kill Rand until the Last Battle makes basic common sense. Every attempt to kill him would likely result in the pattern forcing an advantage for the Light. So they likely expected it to damage his mind, but not end in long term capture. I don't believe a that they could have predicted the True Power use. That exceeds plausibility.

And I still think instintively that using the True Power for the Light ends up being different than using it in service to the shadow -- it's a tool. It might destroy the flesh of the vessel (Rand), but it still wins the battle.