If you couldn't do the Conditional method... Then make 10 of the same hero then every switch increases the level limit everytime you proceed...
10, 20, 30 etc. Which means change main character from Hero Rank 1 to Hero Rank 2
And whenever the main character returns to party. Make common event with a conditional switch.
Name Comment Event: Return Hero
Condition [Level 10 Limit Removed] ON
Hero Rank 2 joins the Party. instead of Rank 1
IF OFF
Hero Rank 1 joins the party. instead of Rank 2.
NOTE: BE SURE TO GIVE THE CHARACTER THE SAME STATS AND TURN HIS HP AND MP to the original rank stats unless if removing the Level Limits heals the character as a reward for passing the first checkpoint.
So make 2 variables for the Previous Ranked Hero's Current HP and MP.
Turn the Rank 2 HP and MP to 1 Then remove the variable by 1 and recover the HP and MP with the two variables...
For the next ranked. MAKE SURE IT KEEPS THE ABILITIES OF THE PREVIOUS RANKED HERO.
Hope it helps!