Sure it's possible but complicated , you have to do 3 layers in eva foam , in the central layers u cut some hole and put blue (and red if you want) leds in it , than u make all cables of leds pass in the handle of the sword where u ve to put batteries and a switch on/off.
You ll do the 2 layers outside with black eva foam and u ll do holes in the same places , than you fill holes with a transparent friendly plastic and you paint it.
your swords are insanly well crafted... any chanse you publish a small tutorial on how you made them? Im building mine on EVA foam with a hollow aluminium rod core so it would be nice to see difrent setups
i dont have any other foto of the work in progress so i cant do a good tutorial .. swords are all maded with polyurethane shaped with a normal cutter and glass paper .. they are made by 2 big pieces , the blade is 2 cm thick and the body is 4 cm. I used a customed pepakura base for the handle filled with polyurethane foam , than i shaped the handle and covered it with a rough string , foam and hot glue for details. Hope it's enough for you