Well, the hero field is called acCshSymbl.
The tag is Hero.CashBackwd.
I don't have the test scripts that I wrote to test it handy, but simply assign a new text value to herofield[acCshSymbl].text and you're good to go. If you want to move the symbol to after the number, add the tag. The timing isn't really an issue, PreTraits/5000 seems to work fine. If you were playing a fantasy game where it was all based in gold pieces, you might do it like so:
Code:
herofield[acCshSymbl].text = " gp"
perform hero.assign[Hero.CashBackwd]