Let's for a moment put aside the issue of DVD Profiler's long term viability. To understand why the function you desire is not in the product, please read the contribution rules. Very briefly, they prohibit the copying of data from other sources without explicit verification by actually watching the movie and / or the credits as displayed in the movie. There are rules about what can be copied from the DVD container, and in some cases, from which side of the container.

That being the case, of course you can put into DVD Profiler whatever you want. You just are not allowed to contribute data that has not been gathered and validated per the rules.

See the "plugins" being offered. Some of them include ways to import other databases (may be obsolete) or derive cast and crew information from IMDB.

This community has always attempted to respect the rules and Copyrights of DVD Profiler and any other programs that we use. My words have not been an attempt to preach; rather to help you understand the context of the limitations that you have noted in your post.