Though after I saw those files, Terez and me argued quite a bit about when they were from (and it's very much open for debate, as many RJ files were partially updated only, retaining bits of outdated stuff). She tended to think it that the "plan" for Taim to be Demandred rather than being his pawn survived for some time beyond LOC before RJ finally changed his mind. I disagreed with her on that.

My opinion is that these two notes belong to the preparatory phase of LOC. They were true enough between TFOH and LOC, but were no longer his plan by the time LOC was finished. One of those quote concerns the rationale for how it ends (Rand's rescue by Taim) and the other concerns the resolution of Asmodean's murder, identifying Demandred as his killer.

I do not believe RJ stuck to that plan until the final published version of LOC, though I tend to believe he did write LOC with this in mind, then at the end he made cosmetic changes, notably to the prologue. The reason is the very same why we could easily eliminate Demandred as suspect in Asmodean's murder: in the LOC prologue, he doesn't know Asmodean is dead, it's the Dark One who reveals this to him.

The other argument is that in the final version of LOC, RJ rather set things up to send Osan'gar/Dashiva to the Black Tower, where he would oversee Taim yet would be forbidden to reveal to him that he was a Chosen and not a high rank DF (that bit in the Encyclopedia is indeed from the notes, not Harriet's interpretation or some such). That version is of course incompatible with Demandred being Taim, SH would not have sent a high ranking DF with Aginor's strength to openly "oversee" the guy Demandred portrays.

I think that RJ's original idea was for Demandred/Taim to play the role of Osan'gar, that is by having him take control of a retinue of male channelers who would eventually betray and attack Rand. I think the idea rapidly evolved in the process of plotting LOC into making Taim only Demandred's pawn at the Black Tower, but since the betrayal of Rand by his retinue was important, to introduce another player, Osan'gar, to be that traitor.

I think when RJ made that decision, many of the Taim chapters were already written, and he decided that the allusions that Taim might be Demandred he had put in there would work nicely as a red herring. In fact, I think he accentuated them even more (I would have expected Demandred to have enough self-control not to appear blatantly hateful and envious or enter pissing contests with Rand....). He did, however, polish the prologue of LOC to eliminate completely Demandred as a suspect in Asmodean's murder. Was it when he chose Graendal as the killer? We'll never know if the switch happened that early, but by the next book he began planting clues, and to eliminate other Chosen (Sammael, Semi, Mesaana) so that finally only Graendal was viable if the killer was a Forsaken.

I don't think RJ's motivation for canning Taimandred was that people "figured it out". The clues were too blatant, he had to know it would turn immediately into a popular theory. One possible motive is that he decided that he rather liked how Demandred (that he used as a character for the first time) played out in LOC as would-be leader of the survivors, the dynamic with Sem and Mesaana, and Granedal, and it's rather Sammael he would eliminate early. He opted for the best of both worlds, ie: he had Demandred pull Taim's strings instead, and that gave him the opportunity to develop Taim into a full wannabe Demandre with delusions of grandeur as to his real place in the Shadow.