Hi  (broken image removed)
I have this code

//5e c2 01
_as3_findproperty var
//24 00
_as3_pushbyte 0
//68 c2 01
_as3_initproperty var

how can I push a number of two bytes to the variable without corrupting the file?

Well, as the name says pushbyte only lets you push one byte. If you wanna push more than one byte you're gonna need to use pushint or pushshort.
And you'll also need to find an extra byte somewhere so it doesn't fuck up the flow of things

That number is 3 bytes long, 0x4EA1FC, so you're gonna need to find 2 extra bytes there

maybe somewhere outside the loop

I have this instruction in the same file
//2d 06
_as3_pushint 5153276

and want to replace it with the code, so I won't  need extra bytes

24 00 -> 2d 06
//5e c2 01
_as3_findproperty var
//2d 06
_as3_pushint 5153276
//68 c2 01
_as3_initproperty var

but I don't know how to change the value indexed by 06

AFAIK there is no way to change the value of an integer in the constant pool while the game is running. You can, however, change the value in SWF Reader and then use this method.