@Bug-Wash and @Jip
I found a method that works
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_...."
step 5 close the client
step 6 open the map folder, for each file that the file name starts with "neroxis_map..." replace the n with "a"
Step 7 open the scenario.lua file and change "neroxis_map" to "aeroxis_map" everywhere you find it
Step 8 open save.lua file and change "neroxis_map" to "aeroxis_map" in the one place you find it
Step 9 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.
Step 10 re-open the client
You will find this map, it will work, and the client won't delete it
someone more sophisticated than me might come up with a way to give your map a completely arbitrary (custom) name and know how to edit the scmap file to work with that. I'm not really a hex editor guru so I don't know if there are tricks to use to add dead space so you can have a shorter file path than what was originally started with. Or maybe you could use a different program to edit the .scmap file to give it your custom name.