Custom Values field in the Legend option?

Can the Values field in the Legend option have custom metrics in addition to the pre-defined ones, e.g., % change in the last value (between the last and the value before)?

Additionally, can we remove the word “Last” in here? It is taking up a lot of space in the plot when I have multiple curves (“Last” will be repeated in the legend for each curve).

Can I get some help on achieving these custom values?