Ian: I was honestly surprised when I read your original post because I didn’t think you would seriously think that was mastering. So I’m sorry I misunderstood. 
However, while in principle what you describe should be possible, there are some sweeping EQ changes, etc. that should be made in mastering rather than in the individual channels.
Pol: I don’t do a cutoff in the high frequencies. If anything, I do a high shelf filter (I want to say at 2.5kHz) to add sheen to the overall mix. If you are hearing harshness then you may have one of two things happening: you have distortion occurring in the tracks where there is emphasis in those frequency bands; or you have multiple tracks competing for your ears in those frequency bands that may even be causing distortion.
Now that I think about it, however, I do have a LPF on the hi-hat and cymbal tracks. I don’t recall exactly where the roll-off point is, but I think it’s around 15kHz.