I am attempting to create Microcircuit Photomask using Inkscape, however, the program only allows upto 25600% magnification, I might be needing Upto 100000% magnification to create microcircuits. Where do I start from editing to code to achieve this functionality, I would love to commit this changes if I could succeed as well. Pointers to start would be appreciated.

To be honest I think that Inkscape is the wrong tool for the job in this case.

In a previous career I had to design photolithography masks with sub-micron features. I used AutoCAD for that, which handled it trivially (impressive when you consider that the same program is used to design bridges and skyscrapers!). I don't know which (if any) of the free CAD programs would be able to achieve the same, but I suggest looking at FreeCAD and OpenSCAD for starters.

The point really is that you probably want a proper CAD tool for the job. Inkscape is an illustration program with a few CAD-like features, but it's certainly not a full-on CAD program.

I can't speak to your specific technology or use case. But can point to some info on how to write extensions, if you want to go that way: https://inkscape.org/en/develop/extensions/

Depending on where you output the svg file, a crappy hack might be to change the scale in the document properties.

For real-world output, 1 mm scales as 3.77953px, so if you set the scale for mm in the properties panel to 0.00004, you will see mm in the workspace, but you will be working in nanometer scale (if I have the decimal places right). You might need to set the numeric precision in the preferences for svg output to avoid rounding.

To actually accomplish an Inkscape program modification, you could work with a developer or become one.
https://inkscape.org/en/develop/getting-started/

(It would be nice to see a modification where all a user needs to do is add a valid entry in the Programs\Inkscape\share\ui\units.svg file.)