test.cpp

// lib /def:user32.def
// cl /O2 test.cpp /link user32.lib
#include <Windows.h>
#include <stdio.h>

struct PrecisionTouchPadConfig {
	BYTE  LegacyParams[3];
	BOOL  LoadedSettings;

	// 0: No delay (always on)
	// 1: Short delay
	// 2: Medium delay (default)
	// 3: Long delay
	// 4: Turn off taps
	DWORD AAPThreshold;

	// 0001: PTPEnabled
	// 0004: EnableEdgy
	// 0008: ScrollDirection
	// 0080: LeaveOnWithMouse
	// 0100: RightClickZoneEnabled
	// 0200: TapAndDrag
	// 0400: IsTPActive
	// 0800: IsMouseConnected
	DWORD Flags;
};

extern "C" BOOL __stdcall UserGetPrecisionTouchPadConfiguration(PrecisionTouchPadConfig *config);
extern "C" BOOL __stdcall UserSetPrecisionTouchPadConfiguration(PrecisionTouchPadConfig *config);

int main() {
	PrecisionTouchPadConfig config = {0};
	// Must be 0 or 1 for GetPrecisionTouchPadConfiguration to return data.
	config.LoadedSettings = 1;
	BOOL getSuccess = UserGetPrecisionTouchPadConfiguration(&config);
	printf("getSuccess = %d\n  LegacyParams=%02x%02x%02x\n  LoadedSettings=%02x\n  AAPThreshold=%d\n  Flags=%08x\n",
		getSuccess,
		config.LegacyParams[0], config.LegacyParams[1], config.LegacyParams[2],
		config.LoadedSettings, config.AAPThreshold, config.Flags);
	if (getSuccess) {
		config.AAPThreshold = 0;
		BOOL setSuccess = UserSetPrecisionTouchPadConfiguration(&config);
		printf("setSuccess = %d\n", setSuccess);
	}

	return 0;
}

user32.def

LIBRARY user32
EXPORTS
	UserGetPrecisionTouchPadConfiguration @2548
	UserSetPrecisionTouchPadConfiguration @2549

For robustness, use mod = LoadLibrary("user32"), pfn = GetProcAddress(mod, (LPCSTR)2548); and check for null pointers and stuff.