After our discussion in the chat and further investigation, I confirm that before deploying the pipeline it is not possible to select a Compute Profile within the Pipeline Studio. However, you have some available options by clicking at Configure, as shown below:

If you click on Configure, you can change: Pipeline Config, Engine Config, Resources and Pipeline alert. In addition, you can also select the Preview mode and then click on Configure to change the runtime arguments and Preview config (number of records that will be shown).
In case that you need to select your Compute Profile to test your code, I would suggest you to deploy, select the proper Compute profile and run it. If you need to change anything within you pipeline, you can duplicate it and it will take you back to the Pipeline studio where you can edit it. You can achive this as following: click on Actions buttom (located in the upper right corner of the Data Fusion pipeline console), then click on Duplicate.
As a alternative, you can also ask for a Feature request with Google in this link.
gcloud dataproc jobs submit job-command \ --cluster cluster-name --region region \ other dataproc-flags \ -- job-args. Is that what you are asking for ? - Alexandre Moraes