Somewhat. I'm only 4 months into FIRE, and am still coming to terms with the shift from saving to spending. It's a much larger paradigm shift than I anticipated. As such, I'm still running scenarios in order to optimise how we spend.
For example, we have our basic living budget which is quite a comfortable existence with funds for dining out each week and $10K a year for family holidays. This was my expected budget for FIRE if we didn't earn anything more.
Since FIRE, I'm now in receipt of a rather large increase in passive income. I knew it might be coming, but it wasn't a certainty so I didn't plan for it in our spending budget. If we don't spend it, my son will be a multi-millionaire upon our death. So we've decided to go a little bit crazy and increase our expenditures quite significantly, at least for a couple of years.
I expect that most people once FIRE'd will find their assumptions changing, and I'd be surprised if they didn't run scenarios to adjust their spending in order to accommodate those changes.