Replaces a specific character range (1-indexed, inclusive) with a new string.
StringReplacePart["string", "snew", {m, n}]
StringReplacePart["string", "snew", {{m1, n1}, {m2, n2}, …}]
StringReplacePart["string", {"snew1", "snew2", …}, {{m1, n1}, {m2, n2}, …}]
StringReplacePart["snew", {m, n}]
StringReplacePart["Hello world", "XXXX", {1, 5}]
→ XXXX worldStringReplacePart["abc", "x", 2]
→ xcStringReplacePart["abc", "x", {5, 6}]
→
StringReplacePart::repart: Cannot replace positions 5 through 6 in "abc".
StringReplacePart[abc, x, {5, 6}]