Hi Eduard,
You can change nylon strings for gut, or gut for nylon, but there are
some rules to follow. One is that types of strings should be kept
grouped together. For example, the harp is strung with wires in the
bass, then one or more octaves in gut, then the rest of the way up in
nylon. There shouldn’t be types of strings mixed in: a gut string
followed by a nylon one followed by two guts then another nylon. This
would make the harp feel very strange when you are playing it. Another
rule is that if you change the type of string, at least that note will
need to have the mechanism reregulated, whether it’s a pedal or lever
harp. Nylon and gut strings react very differently to the pressures of
the levers or discs.
To continue on the concerns voiced by Carl, someone once told me that
gut strings exert 15% more tension than comparable nylon strings. I
don’t know how or if this was scientifically substantiated. I do know
that carbon strings are so much tighter, if you will, that you should
change to a thinner gauge string than what would be used in gut. The
string supplier should be able to help you with this. Of course, the
harp will need to be regulated after being restrung in carbon.
Paul