You can edit the core as much as you want, it is open source. However you cannot resell it as yours due to it being a licensed product. 

If you do write a separate plugin it is extremely advisable that you open a store.  There are many Oxwall users who are leery of developers who try to sell Oxwall plugins without having a Oxwall store because of so much criminal activity that goes with that sort of thing. So you would be shooting yourself in the foot business wise if you did that. 

The process usually takes a few days to a week. They ask for 7 days. 

Also you need to have a store because all your paid plugins need be licensed under the OSCL License  http://www.oxwall.org/store/oscl ;

Your plugin also has to be under a unique name and also has to pass thru the oxwall validation and vetting process before being approved for the store. 

Dave it's a littlbe bit different, as long as you keep Oxwall attribution and all oxwall hyperlinks in the code and front-end anybody can sell it: https://developers.oxwall.com/license

As to the plugin, Dave +1 plugin approval process take from couple of hours to several days. 

Yes, you can sell you plugin on your website, without using store. 

OK ross thanks for the clarification.. :) 

My misunderstanding of this line 

• This software is open source and can be freely used, modified, and distributed.

I thought freely meant only for free. And not only meaning freely as in "you are free to". 

So yes i appreciate that clarification. :)