Let’s say I achieve an ELO of 2400, and qualify for the International Master ranking. Am I now “IM HeyHomie” for the rest of all time? If my play slips and my ELO goes down to, say, 2200, am I demoted to Master? If I sink down to 2000 am I back to being an Expert?
According to the FIDE (which grants titles like Grandmaster or International Master or FIDE Master), those titles they grant are for life. Note by the way that these titles don’t just require a minimum rating; they also require a set of tournament performances above a certain level.
Those are different from level descriptions like “Expert” or “Class A”, which are descriptions of a rating level…those can certainly go away.
Yes, there’s a difference between chess titles and chess ratings, as Maserschmidt said.
Chess titles (e.g FIDE Master, International Master, Grandmaster) are awarded by FIDE based on performances in international tournaments. (You then pay FIDE a fee to register your title - a nice little earner!)
I’m a FIDE Master. I got this by scoring well in 3 suitable tournaments within a 5 year period. The score I had to get each time was based on the average strength of my opposition (which had to include players from different countries.) There are additional qualification rules e.g. about the time limits (speed chess doesn’t count.)
For example, if you have a 10 player all-play-all (so 9 rounds) including at least 3 International Masters, an average rating over 2230 and a mix of nationalities - then a norm is available! (You need three norms in all.) If the average rating of your opponents was 2450, then a score of 50% (4.5/9) is a norm.
I hope that makes sense. 
Tournament organisers who want to attract players will arrange that all the requirements are met (and that the players know what they need to do.)
I ran a few of these events and here was my procedure…
- Get 3 titled players (and have one reserve) by offering them an appearance fee (perfectly legal.)
- Advertise for players wanting a norm.
- Process the applicants, giving priority to high rating (to get the average rating up) and nationality (any countries will do as long as you have a mixture.)
- Charge an entry fee to the non-titled players which covers the fees and other expenses.
Now by contrast chess rating vary over time.
If you achieve a rating of 2400, then you could plausibly argue you were ‘about International Master strength’.
However if in the next rating list, you dropped to 2375 … well now you’re not!
I believe you need players from at least three different countries for a “norm” event. That’s easy in Europe, and in Canada - it’s easy to get Americans - but what’s the third country?
Our Canadian norm events often have students (studying in Canada) who have a foreign passport (as well as being strong chessplayers). Lacking that - Cubans usually require the lowest appearance fees.