:)

So, you think, once it decoded to characters, it will work perfectly without breaking anything?

Yes, in so much as once Unicode::UTF8 does its thing its done, your perl takes over (with all that entails)

What about utf8::valid(). Will it pass? Will it affect anything?

I think it will "pass" and will not "affect anything", but I don't see how it matters -- by using Unicode::UTF8 you're saying the hell with Encode.pm / utf8.pm , i'll let Unicode::UTF8 take care of everything , so there should be no reason to consult utf8 or Encode

What if I try encoding back to bytes with Encode::encode("UTF-8" .. ?

That ought to work fine as well (call me optimistic)

No, I specified in OP that I need compatibility with any version starting from perl5.8.8.

Yes, I've read this, I understand, and its why I didn't make jokes :) food for thought: Re: Why upgrade perl?, Re: perldeltas - every perl*delta in one file (pod.lst)