$organized =~ s/(\w+)[^(^\d+)(\s)]/z/g;
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In a regular expression [ ... ] is a character set. What you told perl to look for is a word followed by ONE character that is not a '(', ')','^' or '+' and neither a number nor a space character.

Since the first word in your lines seems to be a single digit number (at least in your sample data), it is just coincidence that it isn't replaced. Any word of length 1 will not be replaced. Also any word aka element with a number or any of the other characters above as last character would not be replaced.

In short, if these lines work for you, it probably is just a coincidence

Maybe you should use more variable test data to check for edge cases, for example try:

5 suf 6 va7 7dra de) e+f
ed ed 5z5
nu3 b
+4 s 5 +
33 44 55
z5 zb zzz
zb z5 4zz
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PS: Please reread my first post, I had to correct an error in my regex