Absolutely, you can easily connect more decklights by adding more splitter cables after the first one. You can also branch out from one of the connectors if you do not want everything in a long row "one after another".

There is 100cm between the connectors on the splitter cable, and the deck lights have a 70cm cable on them. This means you have quite a lot of flexibility to place the lights where you want them.

For shorter distances: Let the splitter cable go as an "S" in order for the connectors to come closer to each other.

For longer distances: Connect an extra splitter cable and use every second connection. Adjust if necessary by, as above, laying the branch cable as an "S".

You can find a complete "how-to-guide" for the installation of deck lights here: https://lightson.se/en/pages/installation-decklights