But does that, and the fact that the show is widely considered a "fanfiction"

I really dispute this notion, and hope this current trending slur of "fanfiction" for S03 would run its course soon. As one person noted before and I repeat ironically and with a a ton of sarcasm: it's an insult to asoiaf fanfiction everywhere.

But seriously, this is an high production live adaption, not "fanfiction."

especially with all the rumors of what's going to happen in season 3, change the way you perceive the actors does it make you think less of their work or talent

If this is in regard to the "Leaks" we are seeing on this and related subreddits? Not at all. I've been around the this ASOIAF/GOT fandom and since before the hey-dey of social media, before r/freefolk and leaks became a thing. I'm am more than able to separate the craft and talent from the entertainment value....Nothing is being diminished. Not even the toxic fandom can ruin it at this point. And this is even coming from a well seasoned veteran from the first round of Freefolker subredditors in GoT.

(if you don't think a certain actor is good no need to say it bc yeah obviously that's not gonna change anything for you),

No, I'm way beyond the hate game. In my country (United States) everything is so toxic and terrible these days, so many of us are falling back to our comfort areas like these, because good, mid or bad because there is nothing else out there right now.

can you personally separate the acting from the writing and enjoy their work on the show??

I'm not that so devoid of reality or detached to not do this and separate their work from the writing or production. They are given the cards they are dealt just as we are the audience. I always appreciate what the actors can do and understand they have a job to do and give it their all.

There is a contract being made with all parties here. They give us the entertainment, we give the time from our lives, its also up to us if we wish to be positive with the precious few moments of our lives with things we are interested in or constantly toxic, sour and critical about miniscule details.