U can still use it, but before u uninstall fgo mod to switch, just rename the fgo's folder file in android, then rename to the original folder name after u install a new fgo. So u don't need to redownload data from beginning
I got black screen too, i try other website mods but to no avail, then just reinstall the original without mod and worked at least. Just for login streak, hope BMT will got fixed till next event. I'm glad that right now is deadweek