How to edit avkon2.mif?
Easily
SISContents does the job well. If it is already a modded avkon, just edit it directly. Or if you want to edit the original avkon, you might need to convert it to the older version first. SISContents can also help you with it, just specify 102827CF.dll as an intermediate so that the conversion is done properly.
How to edit sysap.exe and qmltouchinput.dll?
The primary step would be unpacking them, as matthew mentioned. Only one packer exists for Symbian, which is called Petran. Luckily, Petran supports unpacking too. Newcooller made a top-up on Pertan namely Petran GUI, get it to make things simpler.
Then you need to disassemble these binaries. If you know assembler for ARM processor, I can give you a bit of further information. Otherwise stop here because you will not succeed.
then you edit with a hex editor.
Maybe as a sporty challenge - yes, if you know by heart common hex patterns of the main functions