Cogwerk's Ailments! The end of Crit! A glorious new day!

[FishDan]

It can also be used to check a particular person to see if they are a changeling by comparing a bloodbag sample to their current blood.

Instead of forcing the already overburdened BYOND engine to juggle ~40 different types of blood, why not go with the standard blood types, but retain the feature. An encounter might go as follows:

Medic picks up health analyzer to scan the blood-loss victim
In the case that the patient was just another stupid crewmember, the analyzer would spit out the data "Blood-Type: B+"
In the case that the crewmember was a changeling or had been given powers by genetics, the analyzer would spit out the data "Blood-type: B+ [mutated]"
Medic would grab the B+ blood bag if the guy seemed legit, or call security if he didn't, and all would be fine and dandy in either case.

I figure this would work best because it doesn't immediately show the crew that "Hot damn! This man is a changeling!" as it leaves a range of doubt, and it would also make health analyzers actually a bit more useful, as well as not being too much of a burden on poor old BYOND.