While writing a new memory manager is a hard job, installing it in Delphi—once it is completed—is very simple. The System unit implements functions GetMemoryManager and SetMemoryManager that help with that:

type
  TMemoryManagerEx = record
    {The basic (required) memory manager functionality}
    GetMem: function(Size: NativeInt): Pointer;
    FreeMem: function(P: Pointer): Integer;
    ReallocMem: function(P: Pointer; Size: NativeInt): Pointer;
    {Extended (optional) functionality.}
    AllocMem: function(Size: NativeInt): Pointer;
    RegisterExpectedMemoryLeak: function(P: Pointer): Boolean;
    UnregisterExpectedMemoryLeak: function(P: Pointer): Boolean;
  end;

procedure GetMemoryManager(var MemMgrEx: TMemoryManagerEx); overload;
procedure SetMemoryManager(const MemMgrEx: TMemoryManagerEx); overload;

A proper way to install a new memory manager is to call GetMemoryManager and store the result in some global variable. Then, the code should populate...