I think the resistors are a coil of nichrome wire. The resistance of nichrome used for heating elements is well characterized and documented for resistance vs temperature. The problems lie in the junction between the nichrome and the terminals, along with the ratio of nickel and chromium alloy.
Over time and heat cycles the spot weld on the terminals can fail, the nichrome can oxidize and properties change for increased resistance. When made in China, who controls the alloy?
It is possible to make an active current source with transistor, I do that on the low switched side of my electronic ignitions. In normal operation the source resistance is quite low, when the current limit is reached, the current holds at set current limit. The dwell time is controlled also, the current ramps up with time and voltage, properly control that and current is limited. At low RPM extra dwell is required because of significant RPM variations, it is hard to predict a few milli seconds over hundreds of milliseconds.
The standard mopar control box does not control dwell time, it is similar to points, but extends the dwell by limiting the ignition period similar to that of a dual points. The ballast limits the current.
Enough about all that for now, I need sleep.