Perl 5 + -M5.10.0, 43 bytes, 15 changes: score 645

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Perl 5 + -M5.10.0, 43 bytes, 15 changes: score 645: SAFE

17 steps total, 15 excluding code and golf.

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Solution

I noticed that I could have saved a byte on my solution too using:

$_=$!=35;/.(.)..(.). (.)(.)/;say"2ドル1ドル3ドル4ドル"; # code

but only after posting and didn't think it was fair to adjust, a whole 15 off my score!

$_=$!=35;/.(.)..(.). (.)(.)/;say2ドル.1ドル.3ドル.4ドル; # code
$_=$!=35;/.(.)..(.). (.)(.)/;say3ドル.1ドル.3ドル.4ドル; # dode
$_=$!=35;/.(.)..(.). (.)(.)/;say3ドル.1ドル.3ドル.1ドル; # dodo
$_=$!=95;/.(.)..(.). (.)(.)/;say3ドル.1ドル.3ドル.1ドル; # nana
$_=$!=95;/.(.)..(.). (.)(.)/;say3ドル.2ドル.3ドル.1ドル; # nona
$_=$!=95;/.(.)..(.). (.)(.)/;say3ドル.2ドル.3ドル.2ドル; # nono
$_=$!=75;/.(.)..(.). (.)(.)/;say3ドル.2ドル.3ドル.2ドル; # lolo
$_=$!=75;/.(.)..(.). (.)(.)/;say3ドル.4ドル.3ドル.2ドル; # lalo
$_=$!=75;/.(.)..(.). (.)(.)/;say3ドル.4ドル.3ドル.3ドル; # lall
$_=$!=75;/.(.)..(.). (.)(.)/;say5ドル.4ドル.3ドル.3ドル; # all
$_=$!=75;/ (.)..(.). (.)(.)/;say5ドル.4ドル.3ドル.3ドル; # off
$_=$!=75;/ (.)..(.). (.)(.)/;say5ドル.4ドル.5ドル.3ドル; # of
$_=$!=75;/ (.)..(.). (.)(.)/;say5ドル.4ドル.5ドル.5ドル; # o
$_=$!=75;/ (.)..(.). (.)(.)/;say2ドル.4ドル.5ドル.5ドル; # go
$_=$!=75;/ (.)..(.). (.)(.)/;say2ドル.4ドル.4ドル.5ドル; # goo
$_=$!=75;/ (.)..(.). (.)(.)/;say2ドル.4ドル.4ドル.3ドル; # goof
$_=$!=75;/ (.)..(.). (.)(.)/;say2ドル.4ドル.1ドル.3ドル; # golf

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I approached this by first printing out all the 2 digit error messages and looking for words that contained g, o, l and f . Once I had some target regexes I checked if any of them would match code and then refined to pick a regex that would have spaces in (at least some of) the right places. From there I worked manually (because I found it interesting!) to pick a route, although automation would have probably resulted in a better score.