Repotting (with expanded clay)???

I now have a Wilma Big 9 and a Wilma 20.
The Big 9 has (9 x) 18lt pots and the 20 has (20 x) 6.5litre pots.

My plan was to put seedlings/cuttings in the 6.5's under MH to veg, then
Re-pot them into the 18's, under HPS, to bud them.

But expanded clay doesn't get bound into a root/substrate mass (like many growing mediums).
It mostly stays loose.....

Is it possible to transplant plants growing in expanded clay???

Is there any particular technique for doing so???

Many thanks to anyone who tries to help.

It doesn't stay loose if roots fill out big they will bind it up right nice.

When I move a 18lt (4.775 US G) Pot, so I can dip a sample from the res, the clay still seems loose.
This made me a little nervous at the idea of changing pots mid-grow.

This time it isn't an issue because I am using the 18lt pots from start to finish.
But I just got the Wilma 20 and, tomorrow, I go to buy the clay pebbles.....