You can. Weird Al Yankovic makes a living modifying other peoples songs, he's hardly the only parody specialist.The Grimm's are dead, they've been that way for a fair bit of time. Disney can't steal their ideas anymore than a car company steals the idea of the wheel from whoever invented it. Even if they take works from living people and modify them, a story loosely based off another and written from scratch is an impossible standard for intellectual property theft.
Well, first of all, Weird Al lives under the Fair Use clause of the Copyright Act.
Second - Disney can't steal their ideas anymore? Really?
The Bothers Grimm, Jacob Grimm died in 1863 - under modern copyright, their copyright would have extended through the first ten years of Disney, 1923 to 1933. But that's merely indicative.
Because Fantasia was released in 1940, featuring:
The Nutcracker Suite, by Tchaikovsky - who died in 1893.
The Sorcerer's Apprentice, by Dukas - who died in 1935.
The Rite of Spring by Igor Stravinsky. 1971
Dance of the hours, by Amilcare Ponchielli, died 1886
Night on Bald Mountain, by Modest Mussorgsky, died 1881
Five, count'em *five* separate pieces of music - in the public domain at that tome, none of which would have been available under modern copyright law.
And yet Fantasia itself is going to be protected by copyright until - 2035.
So sorry - 5/8ths of Fantasia would have been illegal under today's law. And let's be blunt - Fantasia is *exactly* what would be impossible to make today - seven suites, all of them drawn from a previously existing work, each with different set of heirs to deal with, only one actual living artist (Stravinsky) to work with. If the 18 year old compnay formed by Walt Disney had tried to create it today, it would have been sued into non-existence.
We will never see another Fantasia, because we have made it impossible for a small, creative company to *ever* produce another Fantasia.
And that's a damn shame.