Just found a table which defines after what technology each Wonder obsoletes
For curious (v .05), it's located in data segment (0x2b01) at offset 0x10fe - 0x1129 (word[], offset 0x1100 are Pyramids, 0x1102 are Hanging Gardens, etc.).
To patch Copernicus observatory obsolescence data is located at offset 0x1112, the value should be 0x3a instead of 0x7f.
Original unmodified byte data sequence: { 0xFF, 0xFF, 0x2B, 0x00, 0x14, 0x00, 0x36, 0x00, 0x0E, 0x00, 0x0D, 0x00, 0x1D, 0x00, 0x22, 0x00, 0x7F, 0x00, 0x2B, 0x00, 0x7F, 0x00, 0x0F, 0x00, 0x1B, 0x00, 0x7F, 0x00, 0x7F, 0x00, 0x7F, 0x00, 0x7F, 0x00, 0x7F, 0x00, 0x7F, 0x00, 0x7F, 0x00, 0x7F, 0x00, 0x7F, 0x00 }
I haven't tested if this proposed solution works, but other wonders obsolete so it should work. It just needs a test
Further details can be found easily in OpenCiv1 source code (Transfer-unmanaged-data-to-managed-and-code-cleanup branch, GameState.cs, Building Definitions array).
Original EXE can be patched easily, if anyone want's to play with patching details
@tupi and
@darkpanda come to mind
Cheers