Some countries, if not all, do not require regs to be changed to carry dangerous goods on pax a/c. Though CAO stands for Cargo Aircraft Only what it really means is no passengers allowed when CAO carried except certain exemptions which will be list in the airlines AOC. It is quite acceptable and in fact quite common for CAO to be carried on so-called pax a/c and has been going on as standard practice for well over my 39 years of experiencing it in the various countries I have worked in.