You are correct that it isn't possible to change individual resistance values you can only set them at the component level. The simulation in VeSys Classic was originally designed for automotive vehicles and had to be simple, easy to use and fast which is why many of the settings are general. In the typical simulation scenario's where VeSys is used this isn't normally a problem because the wires have the largest impact on the voltage drop. Another problem when trying to create a simulation model is that there are many real world factors that you just can't account for i.e. Component Tolerances, Build Quality, Corrosion, etc. When I was testing VeSys I compared the results to actual vehicles to my surprise the results from two identical vehicles differed by 6% so for us the ability to configure individual component resistances then became irrelevant.
I guess it really depends on what you are trying to simulate and your reasons for simulation.
The simulation in VeSys 2.0 is more configurable in that you can define individual component resistances but I have found that simulation/setup to be more complicated than VeSys Classic, if you have a recent/valid VeSys Classic license you should be able to download VeSys 2.0 and try it.