TLDR; Yes, it's possible, but with some comments

First of all let's look at the past. Were there people that gained rating of 2400+ after a Div. 2 round?
Turns out this already happened!

The 5 contestants that reached red after Div. 2 rounds are

• demon1999 reached rating of 2439 in Technocup 2017 - Elimination Round 1 (Unofficially Open for Everyone, Rated for Div. 2)
• WYZFL reached rating of 2430 in Educational Codeforces Round 132 (Rated for Div. 2)
• apei reached rating of 2421 in Codeforces Round 840 (Div. 2) and Enigma 2022 - Cybros LNMIIT
• klimmek55 reached rating of 2400 in Educational Codeforces Round 103 (Rated for Div. 2)
• afterall reached rating of 2400 in Codeforces Round 685 (Div. 2)

But of course there is always a catch. Both demon1999 and klimmek55 were already masters when they joined the contests, so I wouldn't count that as reaching grandmaster after a Div. 2 round.

Nevertheless, what about the other three?
They had a rating lower than 2100 before the contest and 2400 or more after. Easy peasy right?

Well, unfortunately, no. As a long time member of codeforces I remember this change in codeforces rating. It states, that new users recieve an additional delta for the first 6 rated rounds they participate in. One could already guess that all the remaining participants reached red in the first 6 rounds. apei and WYZFL in 4 rounds, and afterall in 5 rounds to be exact. This basically means, that they weren't really Div. 2 participants after all, since their accumulated deltas actually make them masters.

One could ask whether it is possible even in theory. This question is hard to answer, since codeforces rating is semi-open and might have some hidden limitations. But I am optimistic in this case, and since we know one user could be worth a thousand cyans, current contests are just not large enough for people to shine. If anyone can prove/disprove this mathematically, please share your thoughts in the comments.