What are different methods of preserving chillies?

Freezing

You can freeze hot peppers. Scotch Bonnet and other thin-walled varieties freeze particularly well, although thick-walled ones can be frozen as well. I think the recommended storage time is 6 months, but I know I've had ones that were fine after a year or so.

So long as you're going to be using them in slow cooked applications, you can just drop them in frozen. For other applications, they might be a little bit mushy.

If you want to cut them up, it's easiest to use a really sharp knife or scissors, and cut them up while they're still frozen.

Pickling

Pickling works better for thick-walled peppers, like the jalapeños. It will also affect the temperature, but as a function of time (the longer, the more mushy they get ... slower for the thicker walled varieties)

The vinegar gives a nice brightness to the peppers which may not be desired in all recipes.

You'll want to cut up the peppers before pickling, to ensure that the liquid gets to the flesh from both sides, but you can leave it in slabs to give more options for later.

Drying

I've had mixed luck with drying peppers, but it might be an issue with the local climate. It generally works better with thin-walled peppers.

Once you think they're dried, you'll want to put them in a tightly sealed glass jar and check for signs of condensation on the inside after a day ... if there's any, they're not dry enough to put away for long-term storage.

To use, you'll either have to pulverize them (to make your own version of 'crushed red pepper), or soak them to soften them up enough to use. You can cut up dried peppers into stripes fairly easily with scissors before soaking, but dicing is a bit of a pain.

I really like Joe's answer. My preferred method for long term storage of any kind of pepper is to freeze it. But, in every case I can think of (that's a lot), the peppers benefit from being roasted and peeled before freezing.

Thick walled peppers do well roasting in the oven or charred on the gas stove; then steaming loose the skins by putting the whole, hot (temperature-wise) pepper into something air-tight. Like this: The Kitchn

Smaller, thin walled peppers also are better frozen after they have been roasted and peeled. Check this out! I'm pretty happy with the results of this experiment: Roasting smaller, thinly skinned peppers - removing peel

Don't lose sight of fermentation as a preservation process. It is the method used to make Tabasco sauce, for example.

I grew a lot of scotch bonnet pepoers and my neighbor suggested freezing them whole. When I am ready to use then in a sause, beans, rice etc., I take out what I need, put them in a plastic bag take a hammer and hammer them until they are crushed. Then you can shake the amount you want into the food you are preparing. I made spaghetti sause the other day using the peppers and it gave the sause a great flavor. The next day it was even better.

I personally think that pickling chillies is the best method as this retains the chilli "taste" and not just the heat as when dried or flaked. I tend do use green chilli's as I feel they have more flavour. A simple pickling recipe is best, so as to not destroy the flavour with too many other spices or ingredients.

Here is a site showing different methods of preserving chillies

I think freezing is the option . I have tried it and it doesn't affect the texture and taste when added to food.