If someone were to take Tonks's hair, as she is a Metamorphmagus, does that mean that they can change their appearance just like her, as Polyjuice Potion copies all of the attributes of the person you are transforming into, or would they only be able to turn into Tonks (with her regular hair and features)?
No. In the books it is clearly stated that you can't become a metamorphmagus, you have to be born as one.
‘Well, you’ll have to learn the hard way, I’m afraid,’ said Tonks. ‘Metamorphmagi are really rare, they’re born, not made. Most wizards need to use a wand, or potions, to change their appareance’
Excerpt: Harry Potter and The Order of the Phoenix: Chapter 3 (The Advance Guard)
Thus, in my opinion, there's no way to adquire the metamorphagi powers, even if only temporarily.
They probably wouldn't be able to change into the Metamorphmagus at all, because Polyjuice Potion is only made for complete human transformation. So if the transformation was successful the person who took the potion would not be able to use the Metamorphmagus powers.
WE DO NOT KNOW
Unless JKR (or some other authorized HP universe property — book or film) says otherwise. Everything else is just speculation.
In my opinion, NO, since Polyjuice Potion is for “appearance” only:
It enables the consumer to assume the physical appearance of another person
Pottermore: Polyjuice Potion
Looking like another person is wholly different beast than obtaining another person’s magic.