Hi Geralyn,
you can see a change set as a smallest unit of modification. So you can't choose what will pushed into the repository from a change set. However, you can create more change sets, that will represent different modifications, in this scenario you can group files on different change sets.
Here is a good guide about how to manage change sets:
https://jazz.net/help-dev/clm/index.jsp?topic=%2Fcom.ibm.team.scm.doc%2Ftopics%2Ft_scm_eclipse_csets.html
I hope that helps you!
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