If I switched my date on my Switch to enter an event code only available on that date in mystery gift and I typed the code in, would I get the event Pokemon/Item or would I not get it? Also, IDK what tags to put.
NO According to the comments, and the question in the comments, the answer is No, because the newer games check the actual time and date using the internet making it impossible to get a past event. Source: Comments and https://pokemondb.net/pokebase/314027/will-changing-the-date-on-my-3ds-mean-can-access-older-events.