I'm not sure about going from Telstra to Univeral on Pixels. Used to do that normally on OnePlus (EU to Global and vice versa). My P7P - also in AU - is unlocked and not carrier-linked.
Does your build have specific Telstra mention in the name? If so, I would assume safety and go ahead with the Telstra build. Or alternatively, you can let the device update noramlly if you're not rooted.
Hope the more Pixel-experienced members here can assist you further.
P.S.: I LOVE how you're been on here since 2008 and this is your first post!