How to change VCL code?

Question

I need (to make some quick and dirty tests) to modify the code of Variants and SysUtils.

What I need to do to \"compile\" the changes?

Answer 1

The problem is you would need to compile ALL of the RTL/VCL against the 'new' units.

Instead modify a copy of the units in question and add them to your project when you want to use them. Delphi should use these over those in the RTL/VCL.