Run, notepad,,, PID
WinWait, ahk_pid %PID%
RB := new RemoteBuffer(PID, 4)              ; для проверки создаём буфер в адресном пространстве блокнота с правами чтения и записи
MsgBox, % Format("{:#x}", RB.ptr)           ; адрес буфера
MsgBox, % GetAccessProtection(PID, RB.ptr)  ; должно вернуть 4 — PAGE_READWRITE

GetAccessProtection(PID, addr)  {
   static PROCESS_QUERY_INFORMATION := 0x400
   hProcess := DllCall("OpenProcess", UInt, PROCESS_QUERY_INFORMATION, UInt, 0, UInt, PID, Ptr)
   VarSetCapacity(MEMORY_BASIC_INFORMATION, size := A_PtrSize*4 + 4*2 + A_PtrSize, 0)
   if !res := DllCall("VirtualQueryEx", Ptr, hProcess, Ptr, addr, Ptr, &MEMORY_BASIC_INFORMATION, Ptr, size)
      MsgBox, % "Error: " A_LastError
   DllCall("CloseHandle", Ptr, hProcess)
   if res
      Return  NumGet(MEMORY_BASIC_INFORMATION, A_PtrSize*4 + 4, "UInt")
}

class RemoteBuffer
{
   __New(PID, size)  {
      static PROCESS_VM_OPERATION := 0x8, PROCESS_VM_WRITE := 0x20
           , PROCESS_VM_READ := 0x10, MEM_COMMIT := 0x1000, PAGE_READWRITE := 0x4
         
      if !(this.hProc := DllCall("OpenProcess", UInt, PROCESS_VM_OPERATION|PROCESS_VM_READ|PROCESS_VM_WRITE, Int, 0, UInt, PID, Ptr))
         Return
      
      if !(this.ptr := DllCall("VirtualAllocEx", Ptr, this.hProc, Ptr, 0, Ptr, size, UInt, MEM_COMMIT, UInt, PAGE_READWRITE, Ptr))
         Return, "", DllCall("CloseHandle", Ptr, this.hProc)
      
      this.hHeap := DllCall("GetProcessHeap", Ptr)
   }
   
   __Delete()  {
      DllCall("VirtualFreeEx", Ptr, this.hProc, Ptr, this.ptr, UInt, 0, UInt, MEM_RELEASE := 0x8000)
      DllCall("CloseHandle", Ptr, this.hProc)
      DllCall("HeapFree", Ptr, this.hHeap, UInt, 0, Ptr, this.pHeap)
   }
   
   Read(size, offset = 0)  {
      (this.pHeap && DllCall("HeapFree", Ptr, this.hHeap, UInt, 0, Ptr, this.pHeap))
      this.pHeap := DllCall("HeapAlloc", Ptr, this.hHeap, UInt, HEAP_ZERO_MEMORY := 0x8, Ptr, size, Ptr)
      if !DllCall("ReadProcessMemory", Ptr, this.hProc, Ptr, this.ptr + offset, Ptr, this.pHeap, Ptr, size, Int, 0)
         Return, 0, DllCall("MessageBox", Ptr, 0, Str, "Не удалось прочитать данные`nОшибка " A_LastError, Str, "", UInt, 0)
      Return this.pHeap
   }
   
   Write(pLocalBuff, size, offset = 0)  {
      if !res := DllCall("WriteProcessMemory", Ptr, this.hProc, Ptr, this.ptr + offset, Ptr, pLocalBuff, Ptr, size, PtrP, writtenBytes)
         DllCall("MessageBox", Ptr, 0, Str, "Не удалось записать данные`nОшибка " A_LastError, Str, "", UInt, 0)
      Return writtenBytes
   }
}

https://msdn.microsoft.com/en-us/library/windows/desktop/aa366775(v=vs.85).aspx

VirtualProtectEx(hProcess, lpAddress, dwSize, flNewProtect, lpflOldProtect) {
    if(!hProcess) {
        ErrorLevel := ERROR_INVALID_HANDLE
        return 0
    }
    
    dwRet := DllCall("VirtualProtectEx", "UInt", hProcess, "UInt", lpAddress, "UInt", dwSize, "UInt", flNewProtect, "UInt *", lpflOldProtect)
    if(dwRet == 0) {
        ErrorLEvel := ERROR_FREE_MEMORY
        return 0
    }
    
    ErrorLevel := ERROR_OK
    return dwRet
}