If it's in the same scope, yes.

Not sure what header means for you.

> Can I write "no feature 'bitwise';" inside binary2decimal() to make sure it doesn't misbehave?

Theoretically yes, try it out.

Better use feature bitwise and change the operator to |. ... But this wouldn't work in older Perl.

So in case backwards compatibility is an issue, maybe no combined with if Version >...

In general, if someone was copying that code into his scope, you shouldn't be bothered about their fate. It's their responsibility.

The right approach of sharing code is to use modules, not boilerplating.