No, this feature is only available in Pokemon Emerald.
Well There is no way to rematch the gym leaders unless if you hack it!
You can't rematch them unless you start again
U can't
No unfortunately :(
You cannot.
Hackless, NO!
You cannot.
You can rematch all 16 gym leaders at the Fighting Dojo near the Saffron Gym, you may have a rematch against the gym leaders only when you got their Poke-gear No., while they are away from the gym at a specific time each week also the rematch is in a specific time (ex. Whitney is missing from the gym any day on 12:00-16:00, go to the Goldenrod Dept. Store 6th floor and get her number, her rematch call is on Saturday Afternoon )
WARNING THIS ANSWER IF FOR RUBY, SAPPHIRE AND EMERALD ONLY! 1: Beat the ELITE FOUR. 2: Walk around until they call. 3: Beat the buttsauce out of those GYM LEADERS! CAUTION THEY WILL NOW BE DOUBLE BATTLES.
go to serebii.com it tells how
america
You'd have to use cheats.