Legally the tenant MUST PROVIDE ACCESS for repairs, however, if the tenant refuses (changes the lock), the landlord can break the door down and run the risk of being arrested by the police or going to court which can take weeks or months.
About 32 years ago in my first apartment I was burglarized, I suspected it was the s kids or their friends. I changed the lock and for the next 10 years never had another burglary although others on my floor did. Likewise, I never had a problem with either the landlord or the super about access.
The Tenant should weigh his options but if he want to deny the landlord or anyone else access to his apartment changing the locks maybe the best option in the short term although in theory the tenant runs the risk of either the door being broken or eviction.