Alter list of blocks on admin page
You could try using hook_block_access to restrict access to block operations.


  Control access to a block instance.
  
  Modules may implement this hook if they want to have a say in whether
  or not a given user has access to perform a given operation on a block
  instance.
  
  string $operation: The operation to be performed; for instance,
  'view', 'create', 'delete', or 'update'.