Historical Project Mod Plus (HPMP) is a stand-alone update built upon HPM 0.4.6.3, building upon it with both bug fixes/QoL improvements, and an Expansion of several HPM mechanics I really liked, but felt underdeveloped. Many improvements towards the late game.
I tried creating a hidden reform with the same rules as planned economy, and it seems to work and override the party policy rules, so you all can have fun with that, no idea how unbalanced it is.