I'd probably use look-arounds for what you need:

#!/usr/bin/perl
use warnings;
use strict;
use Syntax::Construct qw{ \K };

while (<DATA>) {
    s/ (?:clothes|something) # Starting keyword.
       \K                    # Don't include the previous part into th
+e replacement.
       (.*?)                 # The part to be quoted.
       (?=\.m)               # Followed by ".m".
     /'$1'/xg;
    print;
}

__DATA__
abc clothes doing shopping at the .m abc something doing shopping at t
+he .mabc
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]