Quick question

He may want to change an instruction to do something else. Like, if you ever find the address that holds the amount of ammo you have in any FPS game, there will most likely be another instruction writing to it.

@OP

I will use Minesweeper and the number of mines as an example.

Address 1005194 holds the number of mines. In CE, you can find what instructions write to which address. I got 0100346E.

The instruction is:
Already, you can tell what needs to be done. I think an easy way to change the value of EAX would be to create a jump. From there you can add another instruction before the one mentioned above.

In C++ I guess you could create a DLL and inject it. Create your own function and jump to it. After you've created the jump of course.

[php]

DWORD address = 0x0100346E;

void myFunction()
{
__asm
{
mov eax,1
add [1005194],eax
ret
}
}

void Jump()
{
DWORD* FunctionAddy = (DWORD*)myFunction;
*(BYTE*)address = 0xE9; // jump
*(DWORD*)(address+1) = ((FunctionAddy-address)-5);
}

//Dll main crap.

DLL_PROCESS_ATTACH:
Jump();
break;

[/php]

Don't expect that to work. I'm trying to give you a general idea of how you can modify the contents of EAX. Like Why said, EAX is a register not a value.

Syntax may be wrong. This whole method may be wrong. Oh well.