I would suggest you instead to try to use CompactGUI https://github.com/IridiumIO/CompactGUI/releases
Using "XPRESS 4K" and "skip poorly compressed file types" you will gain between 40% and 50% of space depending on the DLCs installed.
You can compress your current installation, than download a DLC and compress again. Each new compression will skip already compressed and unmodified files.
Don't go behind "XPRESS 8K" options since the other 2 ("XPRESS 16K" and "LZX") will introduce performance slowdowns (especially LZX).
SD cards are generally not recommended due performance and reliability.