The APs are very intimately connected to Golarion (the PF campaign setting), some moreso than others. The degree to which they can be adapted to other campaign settings easily varies accordingly.
Which would be most easily adapted to Greyhawk, IMO:
Difficult (requires substantial tweaking of story elements to fit)
Runelords triad (Rise of the Runelords, Shattered Star, Return of the Runelords): Relies on the backstory of the Runelords, whose history is directly tied to Golarion and would be difficult (not impossible) to fit into the fairly extensively detailed history of Oerth.
Ruins of Azlant: Like the Runelords series, this one is tied explicitly with the history of Azlant and the Runelords. It would be a little less difficult to retrofit into Greyhawk, the biggest issue being to find a location for a lost (now sunken) culture.
Second Darkness: Fundamental story element is a representation/interpretation of the nature of the drow that is incompatible with Greyhawk lore as it currently stands.
Tyrants Grasp: I'm going to toss this one in this category, since it deals with Golarion NPCs whose history is very connected to that world, and who- while they have semi-counterparts on Greyhawk- don't fit neatly enough with them to make a direct 'or
Moderate (requires some degree of tweaking of story elements)
Jade Regent: As this adventure requires overland travel to an Asian style region of the world, one would need to firmly establish where such a location is relative to the Flanaess (even if using Kara-Tur or something similar), as no such region was ever canonically established. Otherwise, not really too difficult.
Reign of Winter: This one involves a lot of jumping around to different areas of Golarion, as well as other planets, not all of which would necessarily fit into canon locales very easily. One key location- Irrisen- doesn't have a very direct counterpart on Oerth.
Hell's Rebels and Hell's Vengeance: Both of these deal with different adventures in the same location on Golarion (Cheliax), and tie directly into events and histories of that realm. They could probably be relocated to the Great Kingdom without a bit of work.
Wrath of the Righteous: From a thematic standpoint, this could work by relocating it to somewhere like the Empire of Iuz. However, one of the premises of the AP centers around a Macguffin that is not present in the Greyhawk world (the wardstones of the Worldwound).
Ironfang Invasion: Probably could be set in/around the Pomarj, although the histories of the nations surrounding that region don't quite match with the historical conflicts of the regions it takes place in on Golarion.
Iron Gods: The underlying premise is already basically that of module S3: Expedition to the Barrier Peaks. The biggest issue would be fitting in the semi-technological/magical nation of Numeria into the Flanaess. Greyhawk's Blackmoor doesn't as readily fit the bill as, say, Mystara's Blackmoor would. If you don't mind messing around with the Valley of the Mage, I'd say just use the Barrier Peaks location for the crashed ship, and subvert the Vale into the technomagical society described in the AP.
Skull and Shackles: The Hold of the Sea Princes comes to mind as the most immediate location, but some accommodations would need to be made for geography of Greyhawk if putting this there (the AP is set on a series of islands, not a more substantively landlocked area, and there is no maelstrom phenomena on the scale of Golarion's Eye of Abendego on Greyhawk that I am aware of).
Easy (requires little tweaking of story elements)
Legacy of Fire: Elements of this already parallel Greyhawk lore in a lot of ways (particularly some developed in another Paizo AP, Age of Worms)
Kingmaker: Some historical elements would need to be tweaked, but this already takes place in a relatively remote and (purposely) undeveloped part of Golarion. The kingdom building and mass combat mechanics could be replaced with other systems (Dominion and War Machine rules from BECMI, for instance, or Battlesystem for AD&D), or used as is.
Carrion Crown: The biggest challenge would be finding a suitable location, IMO. The underlying goal (prevent the resurrection of a Golarion-lore NPC- the Whispering Tyrant) could easily apply to Vecna or another similar figure (Acererak).
Serpent's Skull: Dropping this into Hepmonaland would be the easiest; there is currently no Serpent-Man culture/race on Greyhawk, but they could be used as is with some tweaking, or Yuan-Ti could be substituted with a little work.
War for the Crown: Probably not too tough, though no thoughts/locations immediately come to mind.
Giantslayer: This one I do not own, but at a guess from what I know of it, it would probably fit into the Sterich/Geoff region (not unlike the Against the Giants series).
Strange Aeons: I honestly don't recall enough about this one to make a guess. This was the "Cthulhu mythos" AP and I very much was looking forward to it, but it felt very bland in execution. I think it probably can be fit without too much effort, but dunno.
Mummy's Mask: This one is connected to a period in Golarion history that could be connected to the Suel Imperium, possibly, but I don't recall enough specifics offhand to say.
Curse of the Crimson Throne: Probably not tough, it's just figuring out an appropriate urban location for it, I imagine.
Council of Thieves: Same as with Curse of the Crimson Throne. Istivin might be a good spot for this.
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