With your blacklist you will boot into r8187Now to switch back and forth between drivers just edit the blacklist file to contain blacklist "blacklist rtl8187" or "blacklist r8187" respectively "Im sure there is a better way than rebooting so if someone wants to fill me in im all ears"
If you don't want to reboot just do this to go back and forth:
rmmod r8187 && modprobe rtl8187 ( to rtl8187)
rmmod rtl8187 && modprobe r8187 (to r8187)
If your Alfa hangs unplug the USB and do then just a modprobe ie of the device you want. Lot faster then a reboot.
Best to ya