I have the basic set and found a way to cheat around it.
If you need to do custom decals, copy and paste the picture you want into the Testors Decal Maker software. You can't import or open them because it is standard version, but you can open the picture up in a picture viewer, (the default in Windows is Microsoft Picture and Fax viewer) go to edit in the top menu bar, click on copy, open Decal Maker, click somewhere on the screen and hold down the CTRL key and press the letter V... works just as well as the upgraded version! Then just resize the picture to fit what you want!
Word of caution... try printing them on plain paper and cutting them out and holding them on the model to adjust for size BEFORE doing it on the decal paper... you have to work with the size a lot to get it where you want it. And if you want text you have to manually enter the font size instead of choosing from the drop down list. I found a font size of 2.5 was good for what I was making the last time I used it, (will vary depending on plane, just play and find what works for each decal). The smaller font sized are not listed in the drop down font size bar. (just drag the mouse across whatever font is listed and type in the size you want)
Good luck!