What is the ruling on purchasing less than a 50% share in a foreign company that displays advertisements containing unlawful music, and is it permissible to request the disbelieving owner of the company to change these advertisements?

Some scholars dislike partnership with those who do not avoid the unlawful, such as disbelievers, because they do not guard against usury and the like, and thus introduce unlawful elements into their partner's share. Therefore, you should not partner with such individuals. However, if you do, you must advise them. If they respond, then that is well and good. Otherwise, ending the partnership is better than remaining with them, lest unlawful elements come to you.