I admit that I do refactor other's working code, but only if:

• We are using a version control system,
• The change is small and contained, and
• We have a decent test suite.

For example, one change I am forever making is to get rid of escaped quotes within a quoted string. I consider this hard to understand:

print "I said \"Hi\".  You said \"Bye\".";
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But, this is much easier to understand.

print qq{I said "Hi".  You said "Bye".};
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