For us the change was not just to live in Costa Rica but to live in the country instead of the city. So some of the changes are just living a different lifestyle in the campo vs. the city. In that sense, I have lost nearly 5 inches off my waist since moving here because I am constantly working on our finca, planting trees, digging a drainage ditch, sweeping or mopping the porch or ceramic inside, putting fertilizer, supervising my caretaker, and so on and so forth.
I went from sitting at a desk in a dark cold room all day to being outside most of the time! (except when it rains)
As to "customs", getting up earlier is one of the things we have learned to do, due to the 6am light/6pm dark schedule year-round.
As TerrynViv said, patience is one thing you have to learn here. I am not saying I AM patient but am trying to be more so.
One thing I'm getting used to is how people want to talk, here. That is, like at a store or anywhere, really, sometimes people just like to talk and I may be in a hurry but I am learning to not be in so much of a hurry and just talk to people when the opportunity arises. Admittedly sometimes I find it a little annoying as I am accustomed to focusing on "getting things done" as opposed to dilly-dallying. But I am learning that sometimes it is rewarding to just take the time to talk to people.
On the negative side- at least in our expe rience - it is customary for workers not to do good detail work (i.e. they don't "finish a job" in a fine way as Americans are accustomed to).
So we've learned that either we have to finish it ourselves or supervise them very closely to make sure it's done right. But sometimes it's hard to get them to do it right even with close supervision. So I guess you could say we are becoming accustomed to not having things done exactly perfectly. Instead of getting mad about it we just go "Oh well, I guess they just don't really "get" that these details are important to us." Like having a shelf completely level or putting silicone sealant around the window neatly as opposed to messily - stuff like that. Most of the time we now supervise closely and in a polite way get them to put a little more attention to the details, and that works out better.
We've learned to drive super defensively because people walk in front of you, drivers stop in the middle of the road, trucks take their lane out of the middle, and people just generally drive like maniacs. This is not just me saying this, my Tico friend says the same thing. I suppose it may depend on where you live but I've driven hundreds of miles in various parts and I have found this to be universally true:
Ticos are lousy drivers.
So I drive way more defensively, and expect a problem at any time. It's dangerous and thus stressful to drive here imho and I avoid it as much as possible.