Two new features here. First is the "Add New Frames" button. This will allow you to build on your sheet even after loading in your initial files.
Click it, and you get a new browser window. Select your files, click open, and...
The program inserts them into the file! Neat. Now you'll also see that the program will now display the file path (unless you loaded a .ssh file, which doesn't contain that data), and there's a "Browse" button underneath it. You can use the Browse button to change which file a texture draws it's data from. Note that if you load a .ssh file, and then use this to replace all the textures, you may save it as a .ssp or .ssl.
So using that feature, I've replace the first sprite with my sprite of Link.
The main point of this is so that you can fix broken .ssl files without trying to remember what the original file path was.
I've also fixed a bug with saving of .ssl files, and added the number of columns to the save data for each filetype. You can still load older files, though, since the columns will just default to an approximation.