Is there any way to make [ and ] hotkeys from Hammer, that change size of grid to 16/32/64 etc?
There is currently no Hammer-specific grid +/- key.
But to accommodate the Hammer users, I'll add that into WW in the next update. Until then, you can right-click the 3D Snaps toggle button in the main toolbar and change the grid spacing in the Home Grid tab. Also, in Anvil's displacement tab, there is a drop down for Displacement Length. If you change that value and hit the Grid and Snap button, the grid size will update.
Also, there is a native Max feature that mildly helps you accomplish this automatically. If you open the Home Grid settings, you can turn off the Inhibit options. When off, the grid will adapt to your current viewport zoom (so zooming out automatically increases spacing, zooming in decreases spacing).
Anyway, I've already made Macroscripts to accomplish it manually, and they will be in the next WW update.
I just updated WW to include this function. Enjoy. The functions are under the wallworm.com category in Max's Customize User Interface. They are called Increase Grid Spacing and Decrease Grid Spacing. They will double or divide by 2 the currently active grid.