Does this part fit the mk2 version of the 550xp?

Thank you for your email. I'm afraid it's not no. You would in fact need the below: 596 35 13 02 - Spike - https://www.lsengineers.co.uk/spike-for-husqvarna-550xp-mark-11-triobrake-chainsaws-oem-no-596-35-13-02.html