Chart legend can’t be customized enough

I have the case of a y-axis where multiple units can be used. Example GB/s vs MB/s

If I have values with low 0 MB/s, medium 500 MB/s and high value 1.2 GB/s, I can only display this as 0 MB/s, 500 MB/s, 1200 MB/s.

I would like to be able to provide a function to format myself the x-axis displayed values, instead of only relying on static sprintf formatting.

This would be most useful for logarithmic y-axis.