In some respects, Derek McKay’s job is like being in opposition. He can commit to spend what he thinks is best, and if the income doesn’t come in, he can point to the UK Government.
As expected, he also suggested that whatever plans are in place are subject to change if and when the outcome of Brexit is known.
If the UK Government has to announce another budget, the Scottish Government will have to follow suit, and this was emphasized both during and after the announcement. Read this post