1. What type of simulation modifier is this?
2. Where can I find the exact SimulationDescriptor Names and Types for this; are there any?
You should be able to define a new SimulationDescriptor for this, though you would probably also have to assign it to all major and minor factions for it to properly take effect. I think the the type depends on what your are applying it to and how you are implementing it. I haven't personally tried to make changes that affect everything, so others probably have more experience with this and can help you better.
3. What about the TargetProperty and Path?
The target properties are the ones PARAdoxiBLE pointed out. Since they are defined on the empire file, the path is most like ClassEmpire.
4. Am I correct in assuming that the operation called for editing the given values would be subtraction and addition respectively?
You could use subtraction (or addition of a negative number) to reduce the values by an absolute amount, or you could use division. Of note here, modifiers are processed in this order:
- Addition and subtraction
- Multiplication and Division
- percentage bonuses (these are added together before being applied.)