def add_suffix_to_fp(file_path, suffix, path_separator='/'):
    """
    Add a suffix to a file name (not a new file type; e.g. 'file' becomes 'file_name').
    Return new filepath.
    """
    new_file_path = ''
    
    new_file_path = file_path.split(path_separator)
    file_name = new_file_path[-1].split('.')
    file_name[0] += suffix
    file_name = '.'.join(file_name)
    new_file_path[-1] = file_name
    new_file_path = '/'.join(new_file_path)
    
    return new_file_path