This is completely impractical BUT has anyone programmed their laser projector to move very slowly in order to engrave an image into something like a black plastic sheet or something else that would absorb the visible light?

I know high power projectors tend to have larger beam specs but they also often have several watts of power so I dont see any reason why it wouldnt work. In theory if you could focus it to a point at some distance you could engrave some decent sized images

I've done it once. I programmed a single point and moved it in a circle over a few seconds. It requires a magnifying glass after the galvos, and the image is limited to an inch or so. (Now that I think about it, it would have been better to place a long FL lens just before the galvos instead.) Anything in the multiwatt range is going to have a poor beam for engraving though, and even the highest power projectors would be on the low end of what engravers can do.

ahh I see. It would be cool if there was a way to get a good point at a distance but maybe thats not achievable.

There is, some laser engravers are specifically designed for that and can engrave VERY fast. I believe they are called raster laser engravers.