I would identify the elements in the module that need to be overridden with custom CSS and do one of the following....

If the module is one place and the amount of CSS is small I may just put it in the header.

If the module is in a few places I would use a page level CSS file.

If the module is all over your site and your site is large then I would have to think about putting the CSS into the skin.

I don't think there are too many other alternatives.

You could go in for modifying the module manifest but I don't see that much of a difference between putting the CSS into the module or elsewhere.

The css was for Invenmanager calendar. It and many other modules have 6 css files. Generally speaking, they want to control my font, H1, etc. I don't want 11 different fonts on my website if I am using 11 modules. Overwriting in skin, means I have 11 useless entries, bloating my css and increasing my page load time.

I like to have Home skin with the essential css for every page, Calendar skin will load home + calendar css, Blog skin, etc. I 'gulp' css and js to cut down on # of css and js files and minify, etc. This also gives you control over order of combining css if there are duplicate entries.

I' m thinking I should take css and js files out of the 'module x' manifest before installing and add necessary files to my Webmatrix solution and gulp/recompile the css and js.

However, sometimes you find some css in a module that just doesn't work (for me) and you want a quick and dirty edit. However, there appears to be no access in DNN to desktopmodules/NameofModule/theCss.css files.