step 1 generate map (repeat as needed until you get one that you want to save)
step 2 open the maps folder (you can use the "hamburger button" at top left of client to do this)
step 3 find the generated map in your maps folder, the map itself is a FOLDER (not a file) and it should be the most recently-created folder in the maps folder
step 4 rename the folder by changing the first letter to an a. It starts with "aeroxis_map...." instead of "neroxis_map_...."
from here, you can close the client if you want. From now on, opening and closing the client won't cause your map to be deleted. BUT it's not ready to play yet
step 5 open the map folder, for each file that the file name starts with "neroxis_map..." replace the n with "a"
Step 6 open the scenario.lua file and change "neroxis_map" to "aeroxis_map" everywhere you find it
Step 7 open save.lua file and change "neroxis_map" to "aeroxis_map" in the one place you find it
Step 8 use a hex editor (such as Notepad++ with the hex plugin) to open the .scmap file. search the ANSI text for the word "neroxis" and change that to "aeroxis" everywhere you find it.
This process is kind of a pain, but if there's a few maps you really like, it will work