I don't knwo what R4 is but I knwo there are map editors for animal crossing. My friend took my save file of of my cartridge and got rid of all the weeds and shit in my town and added a bunch of rare items lying around.
There is a DS homebrew trainer but it isn't that indepth and still beta but the same guy made a Windows App to edit towns and such. I had a little play about with it last year at some point with varying degrees of success. You can get both Here
You need to convert your sav file when you are done editing otherwise it won't work on the R4 because the editing program changes the size of the save file and the R4 won't recognize it, you go here for the converting program: http://www.r4ds.com/soft/2-other-en.htm
***Read this link because in order to be able to use your sav file with the Animal crossing map editor you need to use a hex program with it and edit a number in in real quick otherwise the map editor will give you an error while trying to open it, it really is easy to do after you do it all the first time, it says it's for M3 but it works the same way for R4: