1. If you click on the small arrow, a drop down should allow you directly select from the expressions available in the expression group
Alternatively, use conditional expressions and create e.g. a list box on a data island field or buttons to toggle between your expression (refer to the sample QVW referenced above or search the forum for 'ad-hoc report' to get some demos).
2. You can filter your report either by using a calculated dimension
=If(Year >= 2016, Year)
or using set analysis in all your expression aggreggations, for example something like