one HR we experimented with was “French Resistance”. During the French turn, you roll as if a submarine is potentially damaging each of the 3 French Factory territories held by the Axis (1, 2, 3 = the amount of damage. 4-6 is no result). This provides a reason for the Axis not to take the territories as soon as possible. If they do and they focus their money and attention elsewhere, the factories may have damage or be wrecked when its time for the Axis to start defending against invasion.
The rule was kind of hard to remember to roll every turn, and most of the time, it does very little damage overall.
But, it was part of a set of small changes intended to slow the Axis income but leave choice intact (they can still use their full money for units but if they do, they lose the chance to place units in such advantageous places).
Likewise, and on a different note, we added $1 to Sicily, corsica, crete, cyprus, malta, new guinea etc. to make those have some greater incentive to take them over than just having a new landing spot and denying the enemy one.