Set up a Gold-Per-Turn for Lump Sum Gold trade until the AI accepts it.
Changing the GPT # in the box has NO affect. The AI will accept whatever you put there, but it will still be the original value. And there's no apparent way to 'refresh' the trade.
Example:
I ask Ghandi for a loan of 202 gold for 3 GPT for 90 turns (marathon speed). I then edit the GPT down to 1 GPT. He still accepts the trade, and the trade is for 202 for 3 GPT, not 202 for 1 GPT.