Hi,
I would like to have chdk change the tone of the pictures. Like shifted a little towards green, like old 1970's pictures tend to be.
Can chdk do this with or without scripts?
Not on A4000. On cameras with 10 bit raw, there's a curves feature which might be able to do it, but A4000 is 12 bit. You could technically do it in Lua with
https://chdk.fandom.com/wiki/Lua/Raw_Hook_Operations but it would be very very slow and require programming to achieve the specific effect you want.
Some models have a "My Colors" option in the Canon settings that provides various color effects, but from the manual it looks like this isn't present on A4000. There are some other modes that provide color effects (Live and Super Vivid for example) but it doesn't seem like they'd do what you want.
If you shoot DNG, you can certainly add effects like this using raw processing software.