Change in ETO project after the Quote is accepted

Hi,

We have projects that can take up to 6 or 7 months.

Even after the quote is accepted It happens that there is a change in the scope of the project.

So the quote is accepted , the budget and the estimates are locked. Work has already started and transaction for time and material are posted to GL.

Only planned fields are available for input.

What happens in other industries when they faced with a change like ours.

Do they rely on planned cost only?

Can one create another Project and link the two together? If yes how.

Thanks for your help