/record playerid inputfile outputfile parameters

So, if you're trying to change the gravity of a replay named crabfish and the replay has 700 total frames you'd load the script in utils and then go to singleplayer and type this

/record 2 crabfish outputfile 700


The outputfile line is the name of the replay it will generate(in this case the generated replay will be named outputfile), you'll find the replay it generated in your replay folder where you can then edit the replay in notepad and change the gravity, save it, open the replay in toribash and play with your new gravity.