According to this, you cannot ... SE can only save as itself:
http://www.archicadwiki.com/StartEdition
But, a full license of AC12 can open a SE2009 file...and save it back to AC 11, which can then save it back to AC 10, etc. A lot of work and expect data loss since AC 9 did not have integrated layouts.
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators