Uhh, what exactly is the problem?
The only problem I see in this is that you use multiple build.prop files for enabling/disable stagefright and hardware acceleration.
My suggestion is you use sed, a stream editor. This way, you won't need copying files from the folder and may actually make the code easier to read.
This is how I use sed. It creates a backup of the file, searches for the string to be replaced, and then replaces it.
sed -i.bak 's/ro.media.enc.jpeg.quality=90/ro.media.enc.jpeg.quality=100/g' /system/build.prop
If you plan on doing this, read more about sed. I've kinda forgotten the syntax since I made this 15 days ago and never really used it again. And yes, that's how fast I forget stuff (:
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