Xslt only supports a single input and single output message.
Biztalk provides a trick to allow multiple input messages by concatenating multiple inputs into a single message. However there is no way of getting multiple outputs from an Xslt transform.
Your options are:
1. Debatching the message in a pipeline, although this is based on structure rather than content.
2. Debatching inside an orchestration loop where message content can be used to determine debatching.
Can you explain a bit more about what your requirements are, specifically what is the condition in the input file?