I put ultra-thin Navidrex
grips on my pistol to make it feel not so wide, which technically is customizing it as well.
In my opinion, Hi Power perfection looks like this: a thumb safety you can use on a de-horned Hi Power and a set of either Navidrex
or Spegel grips.
I selected a set of Hogue Cocobolo wood panels for mine; Heinie also offers black Micarta panels from Navidrex
or black anodized Alumagrips--same price--as part of a Double-X package (if you're interested, your local pistolsmith can get a Double-X kit from Heinie for $150, or Heinie/Davis will do the whole thing to your own gun for $300 installed).
If you take the blocky military-style grips off of a BHP and put on a set of Navidrex
or Craig Spegel grips, it becomes not just ergonomic, but alluring to hold.