There seems to be no way to download and inspect the contents of the file once you upload a file (resource) to TIC to be part of your job configuration.
Also it does not seem to be possible to programmatically edit the resource once you upload it. I tried to write rows to a resource and then open and log the output and no rows are ever added but also no error is generated on the tfileoutputdelimited component.
The resource that is used is uploaded to the system where the job is executed. For example, if you use a resource file for a job that is executed on a remote engine, a copy of the file is sent to the remote engine to be consumed by the job.
That's why making a job editing the resource file will not have any impact to it because it will not be propagated to the file stored in Talend Cloud.
You are right that you can see the content of the resource. But as it is said above, the goal is not to modify it.
Introduction to Talend Open Studio for Data Integration.
Practical steps to developing your data integration strategy.
Create systems and workflow to manage clean data ingestion and data transformation.