the is always an official process for interviews (if the school offers them). Sometimes on campus, sometimes with a local alum (who has registered through the alumni office), sometimes either or both. As an alumni interviewer myself, the office makes it VERY clear to us that it is absolutely forbidden to interview someone with whom you have a personal connection.
At some schools you can’t even request an interview until the application is submitted. At others, there’s a deadline in November or so to request an interview. You’ll just have to check the website for the school.
And final point, for many schools (particularly those that fall into the “reach” category) – the interview is often more for the alums to feel “important” rather than having a huge effect on the applicant, unless they come across as a complete jerk 