Density Altitude is pretty much "automatically" covered by the use of hot-wire anemometer Mass Airflow Meters on our cars. The ECUs have a positive/negative 40% fuel trim correction available (actually..more, but the check engine light comes on!) It lives based on what it sees from the wide-band air-fuel ratio sensor. Additional oxygen sensing is performed after the cat to fine tune cruise performance at whatever altitude we are driving. MAFs give the intake air temp very accurately by the data read from their Wheatstone bridge circuit. Many modern cars, that have an outside air temp on the dash, are actually getting that number from the engine ECU, not from a separate temp sensor.
Modifying MAF systems is tricky because you can get outside of the design range of the stock hot-wire MAF. MAF systems for blown engines can require some pretty expensive shapes to cover enough range of air measurement. The problem is that hot-wire systems are most responsive at their lower air flows, and get less "fine" as you get to the max capacity of measurement. That sensitivity at lower flow, to small changes, is what makes them wonderful for emission control vehicles. It also makes them a great tool for your lung doctor...but thats another dizzying story that aint as much fun as racing.
The MAP systems (absolute manifold pressure) also tell the efi what available air is seen in the manifold, but not as accurately at low throttle openings. If the car is a non-turbo or non-supercharged (with a standard MAP sensor), it will be very accurate up to a maximim of positive 4.3 psi in the manifold. The silicone sensing plug will cave in at about that level. Blown/turbo MAP sensor vehicles often have 2-3 bar sensors (2-3 times atmospheric pressure). When you run higher "bar" sensors, you can adjust for more boost, but you lose data points in the wide range mapping. Most of us use MAP systems for racing because they are simple, durable, and cost a lot less.
The MAP systems had to have separate air temp sensors, which you find plugged into the side of the air filter box. For a dashboard thermometer, another sensor was used behind the grill, ahead of the radiator.
If you are running EFI, in feedback control, you will pretty much get "as good as you get". The last cars I saw with an altitude sensor in the ECU were the old P7 type systems with a vane type AFM. They only checked for "over 4300 feet" or "under" because there were different standards for "high altitude emissions" back then. I think there are some altitude sensors still used, but dont know for sure.
Aside from having enough injector capacity for the target HP, you probably wont get in trouble on your EFI tuneup unless you get too big on your injectors. If you cannot run at fairly low (or idle) rpm...at minimum 1.5 millisecond injector duration, you will have trouble.
Intake air temp + manifold absolute pressure ( + intake plenum temp for blown/turbo) = about right for DA
Hope this wasnt too muddy, and it was what you were looking for. If not, "dont shoot the piano player...he's doin' the best he can...". (I saw that sign on a piano in an old saloon in Colorado...how true it is.)
JimL