Thank you very much macropod, just tried it and it worked perfectly! Just what I needed.
One note though, which I forgot to mention earlier. When I run a macro I get a pop-up window reporting "Object variable or With block variable not set" . It is a little annoying but doesn't affect the functionality of the code and I get paragraphs split with asterisks, works just fine.
After playing with it a bit I noticed a small hitch, not too big a problem but anyway. When the chunk of text that makes up one paragraph is bigger than twice (is, say, thrice the size) the value of characters which is set as maximal in the code it won't add two breaks. In other words it can only split in half, i.e add one break per a paragraph. When I run the macro again it adds the remaining break to the rest of the text which now can be split in half. I set the maximum value to 1000 and it doesn't matter much to me personally, I rarely if ever encounter such big paragraphs. And it is not a problem to press macro button a few times more, just in case the document contained some gigantic paragraphs.