Do people in Assam eat beef?

Assamese Hindus usually don't eat beef but they have never had any problem with Muslims eating beef. They even sell their old cattle or male calves to Muslims for slaughter. Cattle slaughter is technically regulated but people don't really follow the law. Assam however do have a mob culture but it is usually reserved for thieves etc. Hindutva mob is a fairly new phenomenon. In terms of religious violence Assam really has only one incident, Nellie. But that was actually more anti-Bangladeshi sentiment than anti Muslim. Hindu Muslim division is not a big thing in Assam, at least it wasn't until recently. But with RSS gaining grounds in recent years it's changing as you can see in the recent video.

To answer last question

The Assam Cattle Preservation Act, 1950 governs the slaughter of cattle in the state. Slaughter of all cattle, including bulls, is prohibited. Slaughter of all is cattle is allowed on obtaining a "fit-for-slaughter" certificate, to be given if cattle is over 15 years of age or has become permanently incapacitated for work or breeding due deformity or any incurable disease.