How to use/define new source formats?

Are those --source-format files even usable for our own data??
For example, if importing demultiplexed data (just paired-end fastq files) following “Casava” part of the importing manual, there is a --source-format with “Casava” in it.
How can I modify it for my own needs???

3 off-topic replies have been merged into an existing topic: Importing the demultiplexed merged data

Please keep replies on-topic in the future.