the experience of those advisors is useless - tell them to sell their tools and look for some other trade to earn their living.
to work neatly on your engine, drain out about a litre of coolant from the system and then remove the upper pipe from the radiator side and then point it down into the same drain container to empty the pipe, remove the flange and at max you will only lose a tea spoon of coolant.
Reason to say this, - coolant is poisonous.
Before installing the bolts back, blow out the coolant with air, blow some WD40 into the bolt holes to drive out any remaining water, blow with air again, makes sure threads are clean and then install the bolts back, A drop of silicone at the bolt neck also helps to keep out moisture leaking into the threads which can rust them out.