Currently you can select all properties or select properties.
In our case we have 30 properties and if we want to select 25 of the 30 we have to click 25 times for each season.
By adding "only" or "everything but" options this would make process easier.
We've got a pending update to support "shift + click" on those checkbox lists. That should be released in the next week or so. We've also got longer term plans to add "select all" and "clear" options to that interface, but I don't have an ETA for that.
We don't allow excluding seasons because it encourages some dangerous patterns for rate calculation. We may revisit this decision in the future, but no plans to change it at this time.