Generally speaking, you can only apply for an ITIN when you have a financial connection to the United States. This is often created when you file a tax return that reports your income or the income of your spouse who is not a US citizen or green card holder.
My question would be, what has changed since the filing of the original tax return that requires you to amend and add an ITIN at the same time? For example, if you were legally married to a non-resident alien but you made a mistake and filed as single, and you now want to correct that and file as married, it would be appropriate and required that you apply for an ITIN for your spouse when you file your return. But to really know how to answer your question, we would have to know more about the exact circumstances.
