To use the password reset flow as a "change password" page, you can create a custom policy that includes a "Change password" user journey. This user journey allows users to change their password without having to reset it.
As for the issue with the "You do not have permission to view this directory or page" message, it could be caused by a misconfiguration in the Azure portal. Make sure that the user flow you're using has the "Reset password" option enabled in the "Password configuration" section of the "Properties" tab. If the issue persists, you can try creating a new user flow with the "Reset password" option enabled.
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