Thank you 
Yes, WiFi card can be exchanged, it is a NGFF type card. I did the same for testing purposes and plugged in an Intel WiFi card which worked nicely. But depending on the card type you may also loose the WiFi kill switch feature - seems that not all NGFF cards support a kill-switch signal. And of course the firmware blob issue… you may need to add non-free repositories from Debian to the PureOS sources list and install the matching firmware package.
Cheers
nicole