Forums Scripts & Popups Help with (simple) text substitution please!

Hi. I've tried looking up examples but haven't managed to figure this out:

I like incoming channel text that looks like this:
[12:57:00] <converter> ( USD ) ( CAD ) +0.31%

to instead look like this:
[12:57:00] <converter> [USD] [CAD] +0.31%

So basically I want to replace "( " with "[" and " )" with "]" on all text in that channel and nothing else. I assume it's done using `on ^*:text:*:#currency:{ ...something here... }`, but I can't figure out how/what.

Many thanks for your help!