This forum probably isn’t the best place to request firmware features like this one. It is best to use the Marlin github issues register instead.
I think someone else has requested something like this already, this link is something similar to what you are after in terms of a firmware change:
Register yourself on github and add to the existing request what you think you need and thinkyhead might tell you what to change.
(Could be as simple as changing the G28 code in marlin_main.cpp near line 7300 to something like:
//gcode_G28(); // comment this C code line out using double slashes as shown