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Is there a way to expand the ROM without making the IPS so big?

I'm guessing if the expanded blank space is at the end of the ROM then the IPS would result in a series of RLE block.

Lunar IPS implements the truncation extension, and might be the first implementation, but we are not sure. Snes9x also implements this extension.

At the end of the patch after the "EOF", the truncation extension appends a big-endian integer of three bytes, to give the length of the patched file. An IPS patcher that implements this extension must truncate the patched file to the given length. The extension does not specify whether this can extend a file.