You can edit the replay in notepad.
Go to your replay folder; C:\Program Files (x86)\Steam\steamapps\common\Toribash\replay
Right click the replay you want to edit and select
Open with...
It should give you the option to open it in Notepad, from there you should see
a lot of numbers n' letters, don't let that be scary.
You should see
NEWGAME 0;500 10 15 0 0 2 270 0 0 classic 0 0 100 0 0 0 1 0 2 0 0 0 0 0 0
500 in this case is the match frames, editing it won't break your replay.
Every other number in that list is either boolean or just a standard setting and follow the order of the game settings.
If you need further help
PM me here on forums.