Toc, HDD Hex Editor did not work for me. I used HexEdit instead, located the text I wanted to change, and did so. Hex Editor was kind enough to offer to disable the 'read-only' attribute of the IO.SYS file and correctly save the changes.
My boot disk no longer starts with the line "Starting Windows 98..." but instead displays the text of my choice. Gotta love it.

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