I never did sth like that, is it easy to do? I always thought standoffs are manufactured IN the case itself and cant be switched (thats how it is with the NR200).
It's super easy, and if my understanding is correct, the Meshlicious would come with similar standoffs to the T1, which used the same Spine System.
Essentially, if you're using a passthrough card like the FE, place your case in the 4-slot GPU mode and offset the GPU towards the side panel with the standoffs. You'll now have space between the GPU and MB for the rear fan to exhaust air into.
That said, it may work better in the T1 than in the Meshlicious, as the former exhausted that air, rather than intaking air from the front - though I suppose you can still exhaust the air instead if you don't mind it blowing at you.