For edit swf file without source code you can use free tool named SwiX
http://swixkit.com
It provides low-level xml view for edit swf.
With SWiX you can open any SWF file in XML format, modify it with a handy preview mechanism and save it as SWF or SWiX file.
For example, change text, font, font size, ciolor, framerate, tune up presentations/banners.
http://www.swixkit.com. There is a sample availabel at their site.
I have succefuly changed text and url of my website swf banner recently using swix tool). Try it.