Here are the steps:
1.) edit the Spotfire WebPlayer component in SF admin UI.
2.) select ‘Edit the Configuration File’
3.) specify the change required. For example, If one wanted to change the max file size from 500MB to 507MB at all places in log4net.config.
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<containerConfig>
<configFiles baseDir="${ENGINE_WORK_DIR}/fabric/webroot/app_data" include="log4net.config">
<regex pattern="500MB" replacement="507MB" />
</configFiles>
</containerConfig>
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4.) click Finish and publish the change to the component from Action Wheel.
5.) Go to Engines > Engine tab. You will see the web player component turned red, indicating component restart required due to change.
6.) restart the component and once its up & running, check the file @ engine’s work directory. For example in this case it was: C:\qa\engine\work\win64vm239-0\fabric\webroot\app_data\log4net.config