Would like to confirm Virtual chassis option on EX4600 devices 

You can set up a EX4600 Virtual Chassis with either:

• A nonprovisioned configuration—The primary sequentially assigns a member ID to other member switches, and determines the role from the primary-role priority value and other factors in the primary-role election algorithm.
• A preprovisioned configuration—You deterministically control the member ID and role assigned to a member switch by tying the member switch to its serial number.

On the following link you can check further information about Virtual Chassis and specifications for this option on EX4600 devices. You can also find step by step on how to configure it: https://www.juniper.net/documentation/us/en/software/junos/virtual-chassis-qfx/topics/task/virtual-chassis-ex4600-cli.html

All configuration committed will be applied/pushed to both members (or to all other members, this in case we have more than 2 members). However, the information will not be seeing as duplicate (this as logically we have just one device, but physical 2) and in case of any failure on the primary device, secondary will be taking precedence and will continue working as the primary.

For Juniper Networks EX4600 series