@Kapelvej 

Hello, theoretically, you can connect a wifi extender to the existing network to boost wifi signal. 

While causing the hotspot may use some special settings, like portal authentication or so, we cannot guarantee that they will work together. 

If you want to extend the wifi signal, you can purchase one to give it a go first.

Note: Please check the warranty policy first, so that you can return it for free with a certain time of period if the extender cannot satisfy your needs.