#MPWC & fopen
You could do this by editing and recompiling the fopen() code in the MPW stdio
library, but, alas, they don't provide source.
That one might need more than 20 files open simultaneously is unlikely, but I
assume you have explored alternatives (such as saving your offset into an open
file and closing it temporarily).
It's also pretty rare that stdio is better for an application than doing file
I/O with the Mac OS yourself.
— F