The problem is these guys don't make the RAM... so even combining Corsair + Corsair is an iffy proposition. For example:
Mushkin Redline DDR4-2400 came with 10-12-12-28 timings using Hynix Modules from start to finish
Corsair DDR4-2400 VP's came with 10-12-12-28 timings using Hynix Modules from start to version 4.51 IIRC. After they switched to a lower cost module supplier and timings dropped to 10-12-12-31
So if you wanted to add to a pair of Corsair VPs, version earlier than 4.51, you were better adding a pair of Mushkins than the newer post 4.51 VPs from Corsair.
However, since we ain't in XMP territory almost any pair of sticks with same SPD settings should work. USe CPUz and look at the SPD tab for your current RAM, than...