No, its not like that. You do not have to give the bayah to a Zaydi imam to be a Zaydi. neither do you have to retake your shahaada or take a ghusl!
It is simply the acceptance of Zaydi creed and jurisprudence to the best of your ability. Once this takes place, you are a Zaydi.
Regarding resources in English, we are working on that and have completed some basic texts. However, the BEST thing to do is learn the Arabic, go to Yemen, and study under the scholars! Nothing beats taking your deen from the men and women who have succesively inherited the religion from their blessed grandfather, peace and blessings be upon him and his progeny!
Until then, we hope that you benefit from two basic texts on the creed and jurisprudence (tahara and salat). Both of them are available on this forum. The first of them is the text on creed, Iqdu at-Thamin. The second of them is a text on the purity and prayer. It is called At-Tajrid. If you cant find them, maybe you can contact the forum administrator and he can help you.
If you have any other questions, please dont hesitate to ask!
And Allah knows best!
Just to add to what (Imam Rassi Society ) Said :
I guess your are from one of the four traditional Sunni school's of thought, and in theory becoming a Zaydi is as easy as changing to a Hanafi if you were Malki or visa-versa.
But the question is why do you want to become a Zaydi if you are still asking a basic question like how to become a Zaydi. Therefore, I think the question you should be asking is why become a Zaydi. Once you have studied this school of thought enough to know if and why to become a Zaydi, the answer to how to become a Zaydi will come natrually.
However, regardless of which school of thought we speak about whether Maliki, Shafi or Zaydi, it is important to note the at the core of each of these schools of thought are what they call “Asool” or foundations which govern ones thought process. So a “Mathhab” or school of thought is a way of thinking.
Some of the things that differentiates the Zaydi school of thought from current Sunni or Imami school's of thought are :
First : it's reading and understanding of history of the prophet (PBUH) and his followers
Two : In “Asool Al-din” aslo know as “Aqeedah” the Zaydis have similar views ( but no the same ) tp the Mua'tazili school of thought
And I think the most important thing to note is regardless of which “Mathhab” or school of thought you associate yourself with you are above all a Muslim.