[PvK]

Hmm. I understand your premise. However I don't think extra PD would help particularly much if the problem is superior enemy units. Also I don't think those specific changes are mod-able. (With mods you can change what and how much PD creates, but not where that PD is, nor how the game charges for it.)

I guess one (complex) way to limit rushes would be to mod in very strong PD, and then change the mod during play as the game got more advanced. E.g., start with the mod giving hugely powerful PD, and every 10-20 turns tone it down until by turn 60 or so, it is back to normal.

You could give nations without "rush" unit types much larger starting armies (though that would make those nations more able to expand quickly). You could also give them some strong immobile starting units, or some starting units which offer a counter to rush units.