You can customize the download folder by modifying the desired capabilities during the execution like this:
import com.kms.katalon.core.configuration.RunConfiguration
import com.kms.katalon.core.webui.keyword.WebUiBuiltInKeywords as WebUI
Map desiredCapabilities = RunConfiguration.getDriverPreferencesProperties("WebUI")
Map prefs = desiredCapabilities.get("prefs")
prefs.put("download.default_directory", "Your location")
RunConfiguration.setWebDriverPreferencesProperty("prefs", prefs)
WebUI.openBrowser('')