I planned to change the package name through smali(reverse)
when I open up apktool.yml, I saw this
forced-package-id: '127'
I have tried to change it but it crash why should i do?
Assuming your goal is to rename the package name of the apk, the package names used for the classes are irrelevant. The package name of the apk is mostly unrelated to the package names of any classes in the apk. And there's no reason you need to touch the package id.
I would recommend unpacking the apk with apktool, and then edit the apktool.yml, setting renameManifestPackage to the new package name. Then when you rebuild the apk with apktool, it should use aapt's --rename-manifest-package functionality to change the package name.
After that, just resign the new apk and you should be good to go.
apktool d app.apk
// change "renameManifestPackage: null" in app/apktool.yml
// to "renameManifestPackage: my.new.package"
apktool b app -o new_app.apk
jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore ~/my.keystore new_app.apk mykeyname
And just to reiterate, you don't need to modify the package names of any classes.