Say you have 1 post on your blog which targets a keyword and you'd like to promote it. Is it okay to write 5 versions of this blog post for ezine articles?
There is no exact and direct answer whether it's okay or not but just make sure that the content is not more or less similar and easily identified as spin-off.
I always advise against just rehashing old material, it ruins your reputation fi you just spew out the same stuff each time. If you write unique articles and this actually builds up your reputation in the field, then this will have a much greater benefit in the long term then finding a quick way to spam up their service.