There is a wiki for this. It is a combo of CLI and editing configs, but you can do all in Luci.

If you consider the MIFI a “tool” then you should be able to set it up once and just change the devices IP as you move from client to client. If you also want it to double as a true router, then it may be best to create 2 config files and do a backup and restore.

In routine operation I will set an expectation that for the dumb AP you will not be able to use the GL GUI tools, but need to use Luci to change the device IP. May be wrong, but you would have to test it.