1) When you see the property value modified or added is not reflecting in application, make sure you are editing the correct config file, eg. editing the s3 datastore config... there could be a possibility the file exists in install location author\crx-quickstart\install\org.apache.jackrabbit.oak.plugins.blob.datastore.S3DataStore.config, however the config values are picked from launchpad config author\crx-quickstart\launchpad\config\org\apache\jackrabbit\oak\plugins\blob\datastore\S3DataStore.config
2) When you see the property values not picked by application specified in the correct properties file, try to change the type for eg. in author\crx-quickstart\launchpad\config\org\apache\jackrabbit\oak\plugins\blob\datastore\S3DataStore.config specifying the value as Integer was not being picked up..
However changing it to string worked (removed I from value...)