The lightbox is just something implemented in the Starterkit as an example. The whole Starterkit is meant as a starting point to learn from how Kirby works, by no means a theme of some sort. It is not part of Kirby, therefore, you will not find anything in the documentation, apart from the basic overview.
In general, the frontend is all yours, so you can do what you like there.
The lightbox is triggered via the data-lightbox attribute attached to the ankers around images, see for example the album.php template. So you could set this attribute based on some condition.
I’m currently working on a Kirby-based client site and found the default/example Kirby lightbox limited for the same reasons.
I replaced this with SimpleLightbox which is still nicely minimal but provides a wee bit more control, including the navigational functionality you require.