DTExecUI.exe is a great tool for building your execution command but it does have a little flaw. There is no UI for selecting a property that you want to set using the /SET option - you have to type it in. Witness here:
Unfortunately that means that you have to learn the fiddly syntax for property paths and quite frankly, as soon as you learn it you are likely to forget it again as you never need to use it anywhere else.
Hence, I haven't bothered trying to learn it because you can get property paths from the configuration wizard. As you can see from the screenshot below of the last screen of the config wizard you will notice that it displays the property path of the property that will be set by the configuration.
Once you've done that its simply a case of copying and pasting the path into DTExecui.exe. Its a bit of a pain in the neck but it works.
If you think having some sort of package browser on DTExecUI.exe would be useful then vote for it here and add a comment.
-Jamie