To not fall in a pit, turn off the PIT flag in all sectors, or turn off gravity.
For impact damage, turn on "No Falling Damage" flag on the surfaces. However, this does not work with objects (3DOs).
Best way is to open kyle.cog, find damaged:
if(GetParam(1) & 0x40
) // If damage type is surface collision
ReturnEx(0); // Don't forward the damage.
Though, a cog on its own that Captures
the player could also work...
I think inside the Rolling Rev mod there is this modification set, though first it checks if a certain Inv is set. Some levels like to turn this collision thing on and off during certain stages.