#SingleInstance force
log := "цукор"
Loop, parse, log
{
    char := A_LoopField
    Loop, 1
    {
        If (char = "ц")
        {
            char := "у"
            break
        }
        If (char = "у")
        {
            char := "к"
            break
        }
    }
    total .= char
}
MsgBox, % total