does anyone have any experience /knowledge doing component wise operations?

mul ft0, ft6.x, fc0.x

Does this put the result into ft0.r, .g, .b, .a? Code like this compiles, but I’m not sure what it does.

You are correct,
mul ft0, ft6.x, fc0.x
is the same as
mul ft0.xyzw, ft6.x, fc0.x
(or mul ft0.rgba, ft6.x, fc0.x)

Shader languages typically allow any kind of component access and they will always compile gracefully.

E.g,
mul ft0.xy, ft6.xx, fc0.yz
is equivalent to
ft0.x = ft6.x * fc0.y; ft0.y = ft6.x * fc0.z

(Please correct me if I’m wrong )
Cheers!
Alex