Answer

What is prohibited here is having different customs in the same place (in the public sphere). In the simple sense, this refers only to public customs (since that is liable to lead to disputes), and specifically within the same community (it is not the physical location itself that determines it). Therefore, nowadays it is accepted to establish several synagogues with different liturgies in the same city, even though the halakhic ruling follows Abaye that one should not have two synagogues in one city.