The new overlay for Smash Soda 4.0.0, do not use it with prior versions. You can now change the position of elements on the overlay with the overlay widget in Smash Soda.
To install this, follow the instructions here: https://github.com/mickeyuk/smash-soda/wiki/overlay
CTRL+SHIFT+C to toggle chat input. When history is enabled you can scroll through past messages with your mouse wheel.
CTRL+ALT+UP/DOWN will adjust the opacity.
CTRL+SHIFT+PLUS will make everything bigger. CTRL+MINUS will shrink everything.