import Foundation
let pattern = #"(?:(:61:[0-9]{1,6}[0-9]{4}C[0-9]+,[0-9]{0,2})(NMSC.+)(\r?\n:86:RGT FACT)|\G(?!^))[ .](\d{5})"#
let regex = try! NSRegularExpression(pattern: pattern, options: .anchorsMatchLines)
let testString = #"""
:61:2204210421C1339,57NMSCTOPF2510474511//GBBK031SCT TOPF2510474511
:86:RGT FACT 17133 TANQ BROERS SA/RGT39370 TANQ BROERS SA48 AVENUE D'ABCDE
:61:2204270427C4808,37NMSCTOPF2520477320//GBJ6009SCT TOPF2520477320
:86:RGT FACT 17274.17442.17546 TANQ BROERS SA/RGT39370 TANQ BROERS SA48 AVENUE D'ABCDE
:61:2203290329C5518,16NMSCTOPF2485471711//GBCJ001SCT TOPF2485471711
:86:RGT FACT.16794 16918 17079 TANQ BROERS SA/RGT39370 TANQ BROERS SA48 AVENUE D'ABCDE
"""#
let stringRange = NSRange(location: 0, length: testString.utf16.count)
let substitutionString = #"$1$2$3INV$4"#
let result = regex.stringByReplacingMatches(in: testString, range: stringRange, withTemplate: substitutionString)
print(result)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Swift 5.2, please visit: https://developer.apple.com/documentation/foundation/nsregularexpression