In reply to MahD:
Actually in the other word,
If I had get_regfile_by_name function:
regfile_name = reg_block.get_regfile_by_name(register_file);
I could write to register field with 5 line code:
reg_block = reg_model.get_block_by_name(block_name);
regfile_name = reg_block.get_regfile_by_name(register_file);
reg_name = regfile_name.get_reg_by_name(register_name);
reg_field = reg_name.get_field_by_name(field_name);
reg_field.set(RegisterValue);
reg_name.update(status);