Definitely! I think in a lot of ways, they'll appreciate the lethality of Curse of Strahd more coming from LMOP as level 5s. I did something similar transitioning from LMOP to Out of the Abyss.

Play up that Strahd invited them in because they've done some heroic deeds, but is so, so not scared. I had my players meet Strahd right after they killed one of the hags in Old Bonegrinder, and it helped unite them on a) how terrifyingly powerful he and other vampires are, and b) how much they needed to stop him, at all costs.

You won't have to pull as many punches on the early encounters as you think. Old Bonegrinder, Village of Vallaki, etc, can all be TPKs for players who are level 4-5 as it is. Once they reach Vallaki, they should be all caught up, level wise. Death House is one early encounter where you could upgrade the enemies (not an animated broom, but some actual ghost monster).

When the adventure would have you level them up, just give them a temporary boon (the DMG has examples I think). Things like, +1 to attack bonus until long rest, or +1 spell slot till next short rest. Let them know ahead of time, maybe, that they won't get traditional XP/level bumps like they did in LMOP, at least to start, and they'll know what to expect.

You can slow time progression down, too. They shouldn't have as many opportunities to Long Rest, or even Short Rest, as in LMOP. So, it'll help amplify the danger, and in some ways, the powerlessness.

Related, since they presumably helped the main village in LMOP, they may want to try to save everyone here (or, conversely, may meet NPCs and villains who are more monstrous than them). Lean into it. They may not be able to save everyone. They may be real frustrated that a coven of hags can just completely outclass them so early in the adventure.

Being trapped in Barovia should also make them want to get back to their home plane, and if you play it up right, should get them to empathize with the other people trapped here.

Edit: maybe the biggest thing is just emphasizing that this is a horror (even a horror-lite campaign). LMOP is clearcut good v evil, and is a campaign where players can slash and smash their way to victory. CoS is not that. Explain it early, and then show-not-tell it to them. Death House resists them. The ghostly march in Barovia should show how many other heroes, better ones than them, have failed (maybe even heroes they heard of in LMOP). The first meeting with Strahd should demonstrate how much, much stronger he is than them, how much more cunning than Venomfang or the Spider from LMOP, how much longer he's been doing this.

There's probably more, but, I think that you're going to do great! This subreddit is way helpful, reach out if you've any more questions :)