New strings will make no difference. What can make a BIG difference is if the string change height from one end of a section to the other. I one had a piano where the difference from #1 to #26 was 5/8". I had the hammers bored to compensate and the regulation was exact and precise. You can even throw a rough regulation on the action before the strings are installed. Do the fine work after. Do not add more than 1 or 2 mm to the bore distance or you will run into regulation problems. Newton
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