How I handled a roommate change without redoing the lease incorrectly

I work in multifamily housing with leases, roommates, and renter's insurance. Recently, I had to resolve a specific case: one roommate was leaving, another was coming in, and everyone wanted to resolve it quickly via email. The symptom that made me investigate it seriously was that there was a shared deposit, old renter's insurance, and joint and several liability on the lease. I preferred not…