Is it possible to modify the article class file?

I would like to write a new class file, preferably from scratch (if that is not way too time consuming). I do not want it to take too long to compile an empty document. The one I have written now uses LoadClass and I think it takes a bit too long to compile my custom cls-file and it is not yet finished.

The base shoule be article. Is it possible to edit the file (and save with a different name)? In particular I would like to define page margins with geometry, change all default fonts with fontspec and also redefine the font size in the [email protected] and also baslineskip and probably many more parameters.

Can I change the article.cls in that way or do I have to write a new class and use LoadClass?