The way you describe a Multi 2D is permitted at Level 4 or 5, but not at Level 2 or 3.
To play Multi 2D at Level 3 it has to be played in a very specific fashion but it is allowed to play it in a wide variety of styles at Level 4.
It is often difficult to know whether tournament is Level 3 or 4 without looking at the advertising. For EBU and WBU events the Level is shown in the EBU or WBU Year book as well.
Roughly speaking the Levels are as follows:
Level 1. Events for beginners and novices advertised as "Simple System" or Limited Conventions" or "Standard English"
Level 2. Bridge Holidays, plus occasional Flight C events, and some lesser Congress side events. Clubs where people dislike conventions, or cater to inexperienced players.
Level 3. Most Congress events, most Clubs. The easier County events, or sometimes just pairs events. Many EBU and WBU events, especially those with shorter rounds. Note that three leading Counties only
run Level 3 events.
Level 4. Many Congress events, some Clubs. The stronger County events, especially teams events. Many EBU and WBU events, especially those with longer rounds.
Level 5. Friday night at the Young Chelsea BC, the EBU Spring Foursomes, and the European Bridge League/EBU Seniors Congress at Brighton.
If you want to know about a specific event I can find out for you.