When you select the shrink-wrap command, and then choose the location you want to save the part. The next thing that comes up will be the shrink-wrap options dialog box. In the upper left there are three options, the default is a composite surface. If this is what was selected then you shrink-wrapped the assembly as a surface and the reason why the presentation file cannot tweak this part file (exported when shrink-wrapped). You will need to try the other two options, either option will create a solid body and you should be able to use this in the presentation. I have attached the dialog box for reference.