Sorry, on the 2x4SFP Uplink Module, you can mix and match 10GE and 1GE. You must set the PIC speed as first step, which is either 1GE or 10GE. From this link - :https://www.juniper.net/documentation/en_US/release-independent/junos/topics/reference/general/uplink-module-ex4200.html
- SFP+ Media Access Control Security (MACsec) uplink module—Provides two ports for 10-gigabit small form-factor pluggable (SFP+) transceivers when configured to operate in 10-gigabit mode or four ports for 1-gigabit small form-factor pluggable (SFP) transceivers when configured to operate in 1-gigabit mode. All four ports on the uplink module are MACsec-capable. The model number of the uplink module is EX-UM-2X4SFP-M.
NOTE: Last 2 sentances do not apply to your situation.
Now on EX4300 Uplink Module this is supported, BUT in order to get this to work you need to reset the PIC after you install the optics. You do NOT set a PIC speed on EX4300. I am trying to get the EX4300 documentation update to reflect this requirement.
Hopefully this assist you.