Try this:
Invoke Replace dialog (default key: ctrl+h)
Find what zone: (?-s)^(.+)\R(.+)(?:\R|\z)
Replace with zone: \1:\2
Wrap around checkbox: ticked or unticked, as you like
Search mode selection: Regular expression
Action: Press Replace or Replace All button, as you like
Here’s how it works:
THE FIND EXPRESSION:(?-s)^(.+)\R(.+)(?:\R|\z)
[Use these options for the whole regular expression][1 ] (?-s) [(hyphen inverts the meaning of the letters that follow)][1 ] - [Dot doesn’t match line breaks][1 ] s [Assert position at the beginning of a line (at beginning of the string or after a line break character) (carriage return and line feed, form feed)][2 ] ^ [Match the regex below and capture its match into backreference number 1][3 ] (.+) [Match any single character that is NOT a line break character (line feed, carriage return, form feed)][4 ] .+ [Between one and unlimited times, as many times as possible, giving back as needed (greedy)][5 ] + [Match a line break (carriage return and line feed pair, sole line feed, sole carriage return, vertical tab, form feed)][6 ] \R [Match the regex below and capture its match into backreference number 2][3 ] (.+) [Match any single character that is NOT a line break character (line feed, carriage return, form feed)][4 ] .+ [Between one and unlimited times, as many times as possible, giving back as needed (greedy)][5 ] + [Match the regular expression below][3 ] (?:\R|\z) [Match this alternative (attempting the next alternative only if this one fails)][7 ] \R [Match a line break (carriage return and line feed pair, sole line feed, sole carriage return, vertical tab, form feed)][6 ] \R [Or match this alternative (the entire group fails if this one fails to match)][7 ] \z [Assert position at the very end of the string][8 ] \z THE REPLACE EXPRESSION:\1:\2
[Insert the text that was last matched by capturing group number 1][9 ] \1 [Insert a colon][10 ] : [Insert the text that was last matched by capturing group number 2][9 ] \2Created with RegexBuddy
[1 ]: https://www.regular-expressions.info/modifiers.html
[2 ]: https://www.regular-expressions.info/anchors.html
[3 ]: https://www.regular-expressions.info/brackets.html
[4 ]: https://www.regular-expressions.info/dot.html
[5 ]: https://www.regular-expressions.info/repeat.html
[6 ]: https://www.regular-expressions.info/nonprint.html
[7 ]: https://www.regular-expressions.info/alternation.html
[8 ]: https://www.regular-expressions.info/anchors.html#az
[9 ]: https://www.regular-expressions.info/replacebackref.html
[10 ]: https://www.regular-expressions.info/characters.html
RegexBuddy settings to emulate N++ regex engine: Application=boost::regex 1.54-1.57 / flavor=Default flavor / replacement flavor=All flavor / ^$ match at line breaks / Numbered capture / Allow zero-length matches