Changing gravity during a replay will break the first part of the replay, as it relies on that gravity, but can be done using the NEWGAME 0; bar with the gravity you set it to,
Teleporting tori and uke is the POS 0(or1); and the first number row is x then y then z
the speed is ANGVEL 0(or 1); and same rule applies
using Nuthugs script however can help with speed,
If you have any more questions or are having struggles you can always pm me.