How to append aapt flags to Android.bp dynamically

I need to dynamically append new flags to aaptflags property from android_app from Android.bp, based in some conditions. I am trying something similar to this answer, the Go script is executed (I can see it when I add some prints), but the flags are not added.

This is my code, any idea what I'm missing?

my_defaults.go

package my_defaults

import (
    "android/soong/android"
    "android/soong/cc"
)

func aaptFlags(ctx android.BaseContext) []string {
    // I will replace this with some logic.
    // Returning a fixed value just for sake of simplicity
    var cflags []string
    cflags = append(cflags, "my_flag_here")
    return cflags
}

func myDefaults(ctx android.LoadHookContext) {
    type props struct {
        aaptflags []string
    }

    p := &props{}
    p.aaptflags = aaptFlags(ctx)
    ctx.AppendProperties(p)
}

func init() {
    android.RegisterModuleType("my_defaults", myDefaultsFactory)
}

func myDefaultsFactory() android.Module {
    module := cc.DefaultsFactory()
    android.AddLoadHook(module, myDefaults)

    return module
}

Android.bp

bootstrap_go_package {
    name: "soong-my_defaults",
    pkgPath: "android/soong/my/defaults",
    deps: [
        "soong",
        "soong-android",
        "soong-cc"
    ],
    srcs: [
        "my_defaults.go"
    ],
    pluginFor: ["soong_build"]
}

my_defaults {
    name: "my_defaults",
}

android_app {
    name: "MyApp",

    defaults: [
        "my_defaults",
    ],

    srcs: ["src/**/*.java"],

    // I need dinamically append new flags here
    aaptflags: [
        "some_flags",
    ],
    
    // ...
}

// ...

Thanks

from How to append aapt flags to Android.bp dynamically