I have set up a chart, and I ultimately want the user to be able to select what variable the data displayed is, but not all variables (in this filter) apply to this chart -so I wondered if it is possible to 'hide' some metrics in a set filter?
Do you mean, as an example, you want to hide fields from the Bar view's "Split" drop-down?
If so, in 2.5, open the drop-down and click the little spanner icon. A "Show" button will appear next to each field. Click to toggle on/off. Click "=> All" to apply to all drop-downs for that field (in all tabs). Click the spanner again, or dismiss and re-open the drop-down, to see the effect as the end user will see it.