"I suppose you want to add support for the J3's external memory."
That is a Yes for this question! And just for external, not both ext and inter.
I understand coding is hard. But in the thread, 2 or more guys proved that it can work on X7, by using El's new resource2.uci. And since the stucture of X7(X7 flash/X7 HDD) and J3(J3/J3 EXT) is almost the same, i guess that it will not be a problem for El to work out a new resource2.uci for J3.
I don't know what *.uci is.
Anyway, I suppose you want to add support for the J3's external memory, right? And I also suppose you've never coded anything in ActionScript, have you? If so, I'll give you a recommendation: Don't even try it. It's not just a simple line like "ADD: External Memory Support" - you'll have to write lots of code and if it was simple, el maco would do it himself.