Much depends how memorable it was before. I'll assume that all the NPCs can stay the same.
Goblins can be plonked anywhere with essentially the same stats, so you just need to tweak anything very memorable from last time; the druid and his firepelt may want to be changed, as might Stickfoot and the warhorse. Ripnugget and Bruzathmus are fairly generic and the bunyip is optional.
I'd put it in an old Thassilonian tower somewhere in Shank's Wood. The only open entrance is high up in the trees, and to get there you have to traverse various flimsy rope ladders and bridges. You can keep the same druid & firepelt, but he commands a mob of wildcats or weasels. The natural way in starts by going through the kennels; the refugees are variously camped in the undergrowth or in the canopy. The lower storeys of the tower are blanketed by thorns so not easy to climb. You can replace the bunyip with a beartrapped, vicious hungry animal of your choice under a flimsy part of the rope bridge.
So cue lots of derring-do swinging through the branches, fighting on swaying rope bridges under arrow fire and other shenanigans. Could be tricky to DM as an extremely 3D running fight, but could equally be awesome. Goblins (being goblins) will do all manner of stupid things (jumping unreasonable distances, stopping to investigate birds' nests for eggs, cutting the wrong end of a rope bridge); encourage the PCs do do likewise.
Then use Thistletop essentially as-is, though you might want to adjust the map if the players have a good memory. Whilst they might realise that they've seen it before, it's just a matter of keeping it a) fresh and b) sufficiently different that they can't metagame.
As the PCs will only be about 3rd level, they won't have any special abilities that'll break it.
Taking it inland means that you might want to change the hermit crab; instead of an outlet to the sea, use a big well or flooded lowest level and put something else in there.
How long ago was it in-game? If it was more than a few weeks, then other goblins just moved in and took over / rebuilt the place. Change up some of the traps and a few of the bad guys. Maybe the new chieftain is a 4th-level sorcerer; replace Bruthazmus with another mutant goblin like Koruvus or maybe a sinspawn with a couple of barbaian levels. Replace Gogmurt the druid with a faceless stalker with an oracle level or two. Maybe these goblins locked an owlbear in the shed instead of a horse. Be creative!
You can then still re-use the map and basic plot.
Meh. There are quite a few areas of RotRL that I'd like to go back and re-play. There aren't really a bunch of big mysteries in the Thistletop section. It's not like the next book, which is one big murder mystery. No, it's just a dungeon crawl.
I'd consider letting your players revisit the area in their shiny new PCs. Sure, the players will recognize what's going on and where things are and they'll remember some monster abilities, but that's not a big deal in the scale of the AP.
You know how many times I snuck the ruined keep from "Temple of Elemental Evil" into one of my campaigns? =^-^=
Just run Thistletop again. Change a couple elements of it to make it less apparent (like maybe a shanty village outside the bridge instead of the thistle maze) and your group will likely not notice it.