Never give your code to anyone. The code is there for security, to secure your device and privacy for yourself and no others. Anyone demanding your code or saying it's "normal" that everyone does it is an idiot living in a fantasy world. There is never any reason for anyone to access your device but you. There is no valid excuse why they should access your device. No matter who you trust today, may not be the person you trust tomorrow. There are endless posts from people who have had problems because someone could access their device.

Resist those who say this is a sign of trust. Today phones and devices are our lives, and for some reason, people think having each others codes means there's some kind of intimate closeness. No there isn't, there's just a huge increase in risk to you and nothing but benefit to them. Why not add them to your checking account while you're at it? Add them to the title of your car?

Nonsense about "changing music" or some idiocy is ridiculous, and the fact that it sounds ridiculous sounds suspicious. You are under no obligation to "trust" anyone beyond the point that you feel comfortable with. Having access to ones device these days means access to all your friends, all your banking, all your thoughts, all your hobbies, and everyone else. Soon questions come of "Who is ABCDEF in your contacts? What was that text about? Oh I took the liberty of editing your photos and uploading them for you. Oh I saw some nudes, who were they for? I sent them to all your friends because I'm mad at you."

If you want someone to have temporary access give them your code, then change it immediately. They don't need it for anything other than the operations you asked them to do.