Is the built in diffuser on the 430ex ii usable or..

can I paint it white since it seems as though a built in bounce card would see a lot more use? I just got my flash a couple minutes ago so apologies in advance if this is a mickey mouse question.

You could just shove a piece of paper in the slot and call it a bounce card ^^

Thats not a diffuser, its a wide angle panel It spreads the light out to cover the angle of a wide angle lens. Do not pain it white for a couple reasons. The primary one being heat buildup. You could fry your light. The second being there are lots of better ways to diffuse your flash, namely a bounce card.

grab a rubber band and an index card

get a $11 Stofen diffuser. they work just fine

Pulling out the wide angle fresnell lens sets the zoom to 14mm, which may not always be what you want.