I've been playing horn for 48 years, and playing the same King Eroica for the past 35 of those. I've never had any customization done, but am investigating a new leadpipe, and would appreciate any input! Thanks!
So much of horn design is a balance or compromise between mutually exclusive issues. Unless you assume the designers of the standard King Eroica leadpipe were incompetent (or unless your original leadpipe has been damaged) what you already have is at at least a reasonable working compromise that will probably give the horn its best all-round performance.
A custom pipe may, for example, emphasise a horn's upper register, giving better "slotting" or clarity, but it will at the same time be poorer in, say, its lower register's response. If you play mainly higher parts, that could be an asset.
However, don't expect there will be some magical all-round improvement with a custom leadpipe. To ensure you're getting the best out of your present set-up, please do check your present leadpipe is totally clean (use a cleaning snake) and likewise your mouthpiece. Maybe also check the rest of the inside of the horn is clean.
If you do decide to go ahead, have a thorough discussion with your chosen designer and find out exactly what the custom leadpipe will do.
I once had a custom leadpipe fitted to a Conn 28D, as an experiment. It improved the register above the stave noticeably; notes were more clearly defined and better in tune - formerly they had been slightly flat. As I was playing high parts at the time, I kept the custom pipe. However, the lower register was slightly less resonant and powerful. When I sold the instrument I sold it with both pipes.