How to not Smart objects can not edit borders tools grayed out

You can easily add a border to a Smart Object.  If you want to add the border outside the existing pixels, you need to add some Canvas to accommodate the border. It can be advisable to add canvas uniformly to avoid the SO being moved from its original location.  

The short answer is don't use smart objects, stick with regular layers. You apparently don't need that level of complexity.

It's always been a basic rule of smart objects that you cannot alter pixels directly in it. No painting, no cloning, etc.

A smart object is a pretty complex thing. It is not the image itself, but a representation of it. An image of an image, so to speak. But that makes a lot of things possible, that wouldn't be possible on a normal layer.

You can either rasterize the smart object, to turn it into a standard regular layer, or open the smart object and do your edits, then close and save.