"The past is already written. The ink is dry."
Time travel in ASOIAF follows Novikov's Self-Consistency Principle, which posits that there is only one timeline, and people who go in the past to change the past have already changed the past and that it was destined to happen all along.
Two major examples in pop culture of other stories that follow this rule. Harry Potter and Futurama.
In Harry Potter, the use of time turners made many people confused. "Why not use them to go back in time and kill Voldemort as a child? Why not save Harry?" Because time travel can't change the past, it can only cause it to happen. When Hermione and Harry use the time turner in Prisoner of Azkaban, they don't change the past by saving Sirius and Buckbeak, they had already saved Sirius and Buckbeak. They went into the past to conclude their destiny to save them.
In Futurama, Fry goes back in time and accidentally kills his grandfather and sleeps with his grandmother. They all expect him to cease existing until they realize that Fry is his own grandfather after all, and the only reason he exists is because he went back in time to sleep with his grandmother (I'll grant that this one is a tad more paradoxical).
Which leaves us with time travel in ASOAIF. Last night, Bran didn't change the past by causing Hodor. Time, fate, destiny....those are written in stone. Bran was always destined to go back and warg into Wylis/Walder, turning him into Hodor. By doing this, it enables Hodor to continue to fulfill his destiny by making him a simpleton who has to help Bran when Bran gets paralyzed.
As for future implications, this means that Bran can't change the past to impact the future. He can't go back and convince the CotF to not create the first Other, he can't stop Ned from being beheaded or Robb from being betrayed. He can only interact with the past to cause the timeline to continue as it already has.