Transferring data between cartridges

So i watched lazy devs' youtube shorts about how he makes his shmup levels. In there he mentioned that he has different pico8 cartridges that work as tools for editing stuff like sprites, bullet patterns and level scenery. I coded a 2d space line editor that can be used for raycasting. How can i transfer all lines data to an another cartridge for use? There is a big "lines" table that containes tables with individual line data. I know that you can't transfer actual code or tables between carts so lazy devs should have used something different.