I have a few lolsome ideas for this movie; First off, we should screw around with their personalities; Like Harry would become stupid, oblivious, and lucky- Whereas Ron would become just outright stupid.
Another idea is to have inside jokes, particularly based around other harry potter crap; For instance, when Hermione meets Harry and Ron, they would say;
"I'm Harry!"
"And I'm Ron!"
"We're gonna bo-"
"We aren't at school yet, Harry!"
And Ron could have a hilarious obsession with bothering people.
Just a few ideas, go ahead and screw with 'em as you wish.