In the classical period of Western music the only generally legitimate ways a composer would appropriate another composer’s music would be to write variations on that composer’s theme or to “transcribe” their work for different instrumentation.
For instance, the popular composer Franz Liszt (1811-1886) transcribed countless orchestral and other works by fellow composers. He recreated them as piano works.
For instance, he transcribed Beethoven’s Symphonies for piano and this actually helped to popularize them. The piano scores were purchased by ordinary people for home performance (many people could play instruments and much home entertainment before the 20th century centured around amateur performance).
See also: variations on a theme