I´am new to the steam community but old to the Age of Empires world, I´ve seen a lot of cool units skin mods, but did not found a mod for the american civilizations sea lines, as its kind of weird to see then in a european fashion.
Ok, its clear that historic accuracy is not the main point for these sea lines, its more a thing of balance, but I think It could get a bit more fashionable.

For an instance, I think that there´s already a mod that can be used as base, the Tzontlimixtli's Greek Ship mod:
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/comments/892247560

These ships, minus the spur and some other little changes could make a great sea line for the american civs.
Some research on this subject: The incas had two main types of ships, the tree trunks sea ship, and the cattail ship, used mostly on the lakes, but also tested in the sea by modern expeditions.
There is evidence that the Inca ventured into the Pacific Ocean and reached maybe even Easter Island, in some of the aforementioned.
Some image links:
kon tiki tree trunks sea ship [ae01.alicdn.com]

kon tiki expedition[www.puranoticia.cl]kon tiki expedition[/url]

totora ship[i.pinimg.com]

Viracocha expedition[kommunikasjon.ntb.no]

In the other hand, there's no evidence that aztecs or mayans do it into the open sea, but its known, from the conquistadores accounts that they used very large canoes (acallis) at war, with dozens of warriors in a single one, used basically as platform for shooting arrows and darts. These could be reminiscent of others known to be used by other cultures. Some iamge links:

salisipan canoe[upload.wikimedia.org]

large canoe[lh3.googleusercontent.com]

native canoe[lh4.googleusercontent.com]

indian canoe[www.donsmaps.com]

As you can see, some of these resembles the ships of Tzontlimixtli's Greek Ship mod. I hope someone takes account my asking, I can help if necessary, I don't know very much on reskining units, but have some skills on image edition.

Cheers!