live-build uses syslinux and some of its derivatives (depending on the image type) as bootloaders by default. They can be easily customized in two ways.
In order to use a full theme, copy /usr/share/live/build/bootloaders into config/bootloaders and edit files in there. If you do not want to bother modifying all supported bootloader configurations, only providing a local customized copy of one of the bootloaders, e.g. isolinux in config/bootloaders/isolinux is enough too, depending on your use case.
There is also the possibility of making smaller changes. For instance, syslinux derivatives are configured by default with a timeout of 0 (zero) which means that they will pause indefinitely at their splash screen until you press a key.
To modify the boot timeout of a default iso-hybrid image just edit a default isolinux.cfg file specifying the timeout in units of seconds and add it to config/includes.binary/isolinux/
A modified isolinux.cfg to boot after five seconds would be similar to this:
An alternative way of achieving the same goal could be writing a hook and adding it to config/hooks/. Remember to add the .binary suffix to run in the binary stage. A proposed example:
sed -i -e 's|timeout 0|timeout 50|' binary/isolinux/isolinux.cfg
Likewise, if you want to use a personalized splash.png image, add a picture of 640x480 pixels to config/includes.binary/isolinux/
When creating an ISO9660 binary image, you can use the following options to add various textual metadata for your image. This can help you easily identify the version or configuration of an image without booting it.