Editing a custom field (metric) you currently have in use is a hassle! When you select the edit button you just get some display options. I need to click "Create new field" in the bottom right. Then from there do "All fields" then search for the field I want to edit, then i can edit it.
For filters this UX is there. If you add a filter to a table/graph then when you hover over it in the list of filters there is a edit button and you edit that filter directly there. Custom fields (metrics) don't have this, they should!
Customer support service by UserEcho