SlickEdit creates tag files for Visual C++ and C# automatically as a convenience to you, so that you have symbol information for the standard libraries and in the case of C#, the .NET CLR. We use the existance of the tag file as an arbiter, so if you just delete the tag file, either from the file system or using the Tag Files dialog, SlickEdit will notice that it's gone and rebuild it.
The best way to cripple these tag files is not to delete the tag file, but to just empty it out. To do this, go to Tools > Tag Files..., select the tag file you would rather not enjoy the benefits of having, and click in the list of files, hit Ctrl+A to select all of the files, then hit "Remove Src. Files". Be patient, it will take a while, because it removes the files one at a time. But in the end you will have an empty tag file that will behave like as if it wasn't there.