I am somewhat surprised at how you are approaching this problem. My guess would be that you are lacking some understanding of basic geometry types.
The NURBS patch layout of the original file as shown in your first post was indicates that this design was created with a Sub-D modeling technique. Only the hole and the zig-zag cut in the tail were later applied using solid modeling.
If the design was originally created in PTC Creo then the base geometry before these solid modeling features were applied were most likely created with PTC Creo FreeStyle, which is a Sub-D modeling plugin for Creo. Similar to T-Splines that Mesh object was then converted to NURBS surfaces or a solid and then the already mentioned solid features were added.
NURBS are also controlled by meshes of control points somewhat similar in concept to the control cage of a Sub-D model or a T-Spline control mesh in Fusion 360. In some 3D software packages after import you can directly manipulate this mesh of NURBS control points, e.g. Solid Thinking Evolve, Maya, Houdini and a few others. However, in Fusion 360 and I would believe also Inventor you don't have direct access to this and as such the smallest element you can work with are the NURBS patches or surfaces.
In Fusion 360 and again I believe this applies to Inventor as well, you can convert a T-Spline into NURBS. You can also convert individual NURBS patches back into T-Splines, however the T-Spline mesh you get from that does not match the control point mesh of the NURBS surface. The only software I am aware of that allows you to export a NURBS control mesh as a .obj is Solid Thinking Evolve.
It looks like you spent some considerable time in inventor to re-design this design with the tools available in Inventor. Now you're stuck with solid modeling and NURBS surfacing techniques, which make the required edits to this painful and slow. For comparison, using a Sub-D mesh you'd be done with these edits in less time it took me to write this post.
As you now have a Solid Model, I am not exactly sure what advise you are looking for and what help you need.