How to change the implementation (detour) of an externally declared function

I have a third party function

function DataCompare(const S1, S2: string; APartial: Boolean): Boolean;
begin
   ...
end;

It is used in another third party unit.

I wish to replace the body of the function at runtime with another new implementation.

Is this possible? I guess there will be a need of some hack (ala VirtualMemoryUnprotect). A non-assembler solution is very welcome.