Just to be clear, that doesn't work if the original expression doesn't start with ^.

>perl -le"print 'abc' !~ /b/ ?1:0"
0

>perl -le"print 'abc' =~ /^(?!b)/ ?1:0"
1

>perl -le"print 'abc' =~ /(?!b)/ ?1:0"
1
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That may not be an issue in this case.