While that works in a private corporation it would amount to nothing more than an empty gesture at the federal level, like Trump refusing a salary.
Uh, no. Let's take food stamps for example. Say that Congress appropriates $80 billion for food stamps, but only $60 billion was actually spent on food stamps. Then at the end of the fiscal year, there should be $20 billion left over, and a sign to Congress that only $60 billion is needed the next year. Instead, the government finds other (non-wall-related) things to spend the excess $20 billion. And then the following year, Congress automatically appropriates $84 billion.
I choose Option A. There is nothing empty about having hundreds of billions of dollars left over in the Treasury at the end of the fiscal year. Those are dollars that can be used to retire debt.