Can I have different goals on different days?

Yes. Open You → Goal and use Different goals by weekday to set the pattern you want. You can also mark today as a training day. Every day's goal must still meet the safety limits.

Review the goal shown for the selected diary day when checking what remains. A higher training-day goal and Health activity should not be stacked to count the same activity twice. These options change the goal. They do not add an invented workout to your history or require a more expensive plan.