Metric relabeling in rancher-pushprox

Hello every one.currently i have a task to create a central monitoring for different order to categorized my cluster which need to be monitor with central monitoring cluster i define externalLabels on each of them. for example:
externalLabels → cluster: dev1 cluster: dev2 and so on…
but the point is how can i define externalLabels for central monitoring itself?because externalLabels only work when external system scrap the metric not it self.i solve this problem for component which is scraped directly with prometheus with metricRelabelings but the component which is scraped with rancher-pusprox is my there any way to solve this problem?