Regarding to your post and solution I have to add my 2 cents because made me scary what are you doing here.

This showing me lack of understanding of how flash player works.
And this solution is useless. You can fool the flash player version number this way but it doesn't mean you can play real flash 10.0 or 10.1 content at all. Do you really think the only difference between those players are the version no.??

First of all. I am working on my flaemo project and have some internal code to recognize witch version you running to be able to prevent situation that entire project will use some non compatible code.

With this solution you are for sure crash flash player. in any other project that using this method.

Secondly if you developing some project and compile it in Flash 10.1 and you are NOT using anything flash 10.1 or flash 10.0 specific you will be able to see whole content as is. It doesn't mean your original flash 9 will run faster. (It must be some placebo effect guys )

I will give you example in pseudo code.

if you running flash 9 use
private var somevariable:Array = [];
if you running flash 10.0 use
private var somevariable:Vector<*>= new Vector<*>
if you running flash 10.1 use
private var somevariable:Vector<*>= new Vector<*>
Multitouch.inputMode = MultitouchInputMode.TOUCH_POINT;

if you fool your flash 9 and pretend you running 10.* guess what will happen. Yes, dead flash player. Otherwise Every project that is not running flash player version specific code will handle this task itself.
You don't have to cheat this way.

There is another one situation.

If in html code somebody added minimum version required is 10.0.0 and in fact swf is not using anything from flash 10 can happily run. The only blocker is html tag. There is simple way around this issue just call swf file directly!. [Or you can use Attilla77's Flash Launcher and you can REALLY see performance improvements.]

So once again I DO NOT RECOMMEND this solution because is useless, will not speed up anything and make even more content unable to run if some project like flaemo has encapsulation of methods that specific player can or cannot run.

Check this out.
go there with this player installed
http://www.flaemo.com/ctest/

Pseudo Flash player 10.* will run the code up to meet some flash player version specific code and will stuck on manufacturer, because next feature required real flash 10.0. witch is obviously not present in your fake player. There is at least tens of features for each player version added. speeding up a lot of things, there is big difference between flash drawing API methods between flash 9 and 10 and so on.
Flash developers are happy to use it since we where asking adobe waiting for all this stuff. Don't fool yourself!