colName = "COLUMNNAMETEST LONG\1NAMESHORTEN2339E0HS111 KEEPTHIS";
Rename_regx = substitute("LONG\1NAMESHORTEN2339E0HS111","\","\\");
Rename_to = "39E \1 0H";
// \Q starts a sequence that ignores escapes
newname=Regex( colName,
"(.*?)(" || Rename_regx || ")(.*)", // match
"\1\Q" || Rename_to || "\E\3"); // replace match with
show(newname); // newname = "COLUMNNAMETEST 39E \1 0H KEEPTHIS";
// notice:
// \Q begins "quoting" and \E ends it
// the \Q has a side effect of ending the \1 (which is what you asked)
// the \1 in the replacement is NOT expanded inside the \Q...\E
// at the very top, it takes care of escaping any escapes with substitute,
// which *could* be an issue
// what else? upper and lower case:
// \L begin lower casing
// \U begin upper casing
// \E ends *all* \L, \U, or \Q
show(regex("aBcDEf","(..)(..)(..)","\1\L \2 \U\3"));//"aB cd EF"
// \l (lower case L) lower case the next character
// \u upper case the next character
show(regex("ABcdEF","(..)(..)(..)","\1 \u\2 \l\3"));//"AB Cd eF"
// the Q, L, and U modes share a common E (end)
// the q and l are not persistent and only apply to the next character.
// upper/lower is probably very ASCII specific, no Unicode magic.
// this is poorly documented here: https://www.jmp.com/support/help/en/17.2/index.shtml#page/jmp/escaped-characters-in-regular-expressions.shtml
// somehow all the escapes have been lumped together in the worst possible way.
edit: there are two parameters to the regex() function that use escapes. Parameter 2 is the pattern and uses escapes the way most people expect, and the \Q \U \L \E \u \l do not belong there. Parameter 3 is the replacement, and the \Q \U \L \E \u \l can be used there. Backreferences \1 \2 \3 ... can be used in both parm2 and parm3.
Craige