Hmm... I think we are both talking about this field:
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At least for me it the Firaxis editor defaults to 2 for most governments, 1 for Anarchy, 3 for Democracy, and 4 for Fascism.
Checking how it's done in my editor, I scaled it so that 2 in the Firaxis editor is 100 in my editor; according to the Civilopedia Republic has 100% worker rate, so "2" is 100%. Anarchy is 50 in my editor, Democracy 150, etc.
The spinners in my editor allow changing it by 50 at a time. If you enter a non-divisible-by-50 value such as 74, it will round it down to the nearest 50:
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Unfortunately, the BIQ format itself limits this field to increments of 50%. There's no way to give a government 120% of the standard worker rate, as far as I know. Perhaps Theov knows something I don't? That could be simulated by having different Worker units that are generated by a government-specific wonder and which have different worker rates as a unit, but I don't know of a way to change it across the board.
Edit: I'm still not 100% sure we're talking about the same field. The "Worker Rate" field has a limit of 20 in the Firaxis editor.
Theov's Expanding Civ3 Mod
notes an Architect unit with a worker rate of 125%, but that can be set via the units tab.