Hyper-V Default switch IP address range change. Ver 1809 Build 17763.1

Well normally those who virtualize servers for real life uses have at least one gigabit Ethernet port, that's the least i can say. the norm is 10 GBit Ethernet(s). not WIFI. and they are always-on connections. that's why we don't see server admins complain about this Hyper-V feature because the proper way would be to create 1-on-1 links between Physical and Virtual network adapters using External virtual network adapter.
I totally understand your situation, sometimes you have to switch between WiFi and Ethernet because it's a laptop, portable and so on.
you can still create persistent routes in the Window's routing table and make the default virtual network adapter's IP address stick even after reboots.

Btw, you Don't have to change anything in the Guest OS if you change your active network adapter from WiFi to Ethernet. all you need to do is to go to Hyper-V's virtual switch manager, go to the external adapter and change the external network from the drop down list. the guest OS shouldn't need any further changes if it has already given a static IP address from the same subnet.