When it comes to pushing ceramic pistons back in on my SLX 675’s is using a plastic tyre lever the right way to do it?

Cheers MT

Yes ,anything will do really so long as it’s soft, like plastic, and not metal that can damage the piston. I usually slide the tool across the piston face and then with it overhanging both sides of the piston I use both hands which I find slides it back in more even.

Do you not do this with the old pad in place?

You can but I damaged my pad last time as I chipped a little off one edge so now I take them out.