Default action bar help
 

Is there a script or addon that can scale the default Blizz action bar UI

Dominos can for sure change the scale of the actionbars, bartender should be able to and ractionbarstyler should too, I think.

Yes, there are script commands you can use.

Put "/script " in front of them when using them in-game or just put them in a lua file and create a toc to make an addon out of it.

Just replace the 0.9 to your preferred scale - 1 is the default setting.