Manhwa with reversible threesome?
http://www.mangago.zone/read-manga/satou_kun_ni_wa_kanawanai_sachimo/
This ones not reversible but still threesome (=・ω・=)
http://www.mangago.zone/read-manga/yarisugi_party_night/
http://www.mangago.zone/read-manga/nibiiro_no_hana_gou/
http://www.mangago.zone/read-manga/harami_bara/
http://www.mangago.zone/read-manga/koitomo_triangle/
http://www.mangago.zone/read-manga/futari_no_musuko_ni_nerawarete_imasu/
This one was the BEST for me
http://www.mangago.zone/read-manga/i_wanna_die_before_i_m_30/
Any threesome manga/manhwa where the MCs switch position?
God, a good threesome manga is really rare to come across T-T But heres one that I know.
http://www.mangago.zone/read-manga/satou_kun_ni_wa_kanawanai_sachimo/
Manga has better art and is funnier than the anime, but when it comes to pacing, it's a bit rushed and incoherent. Anime's pacing is slower, but you can appreciate the plot more. Character development in anime is much deeper. You'll get to know more and understand the characters and the plot in the anime better since it's not rushed.
I commend the anime team for bringing out the best in Black Clover story-wise. It's a much better experience for me, since I lean towards better story and character development than the art.
I remember these were the reasons why I dropped the manga at Ch 40 before the anime started. Everything's just happening so fast. The anime re-kindled my interest and made me fall in love with Black Clover.