You have to know that repair is safe and meets all the coolant system design constraints. It certainly isn’t something most shops are going to just have a standard procedure for. That was what caused the problem in the first place.
Sure you technically have to "verify that repair is safe and meets all the coolant system design constraints". Except you don't, because common sense says most of those constraints are not critical. Like sure, the narrower ID of that 1/4" NPT nipple might cause a little more backpressure to the coolant pump. But there is no way the system would have been designed to be that marginal in the first place.
The main thing to worry about is chemical compatibility of the antifreeze to the new materials, but that's at worst a half hour to find the antifreeze datasheet. Or the mechanic already knows, from seeing the parts of other systems that antifreeze is used in.
