I agree with Polo. You can use these words interchangeably but the most typical way to express this idea in spoken conversation would be the word "like" or even "the way." "As" sounds more formal (that's closer to a literary use) and "how" is more like a slang use, if anything (the way a child might say it) but still perfectly understandable.

You can absolutely use them interchangeably in these contexts. It does slightly impact the formality of your sentence but not by much. For example, "She looks exactly as she did a decade ago" sounds more old fashioned than "she looks exactly like she did a decade ago". I probably wouldn't use 'how' in that sentence, but it would be understood if you did.