"You can attach any weapon to this character, ignoring play restrictions".

Does this allow Finn to attach another weapon upgrade when he already has three upgrades?

No, the max number of upgrades is always 3.
If you somehow happen to have more on a character you have to discard down to 3.
(see Rules Reference page 7 - Upgrades)

good question

The same question has been asked about Unique. So can Finn have two copies of the same Unique on him?

No to both questions.

Page 19 of RR, Play restrictions appear on the card and are marked by the word "only". Unique and Upgrade limit of 3 are a game restriction, no play restriction.

The same question has been asked about Unique. So can Finn have two copies of the same Unique on him?

No to both questions.

Page 19 of RR, Play restrictions appear on the card and are marked by the word "only". Unique and Upgrade limit of 3 are a game restriction, no play restriction.

I was to lazy (tired from a weekend of gaming) to look it up really. But thanks and indeed clear