If you do get tinkering with your harmonicas, you can get no end of good advice from members of harp-l. There are professional harmonica customizers on the list, including some of the big names, as well as experienced and knowledgeable amateurs. They love - and I use the word advisedly - to expound on such compelling matters as the finer points of re-tuning, re-gapping, and re-jigging generally.