I want to put some objects on a wall as decoration but I don't want it to be removable. For some I've found static versions but not for all. Is it hard make a new static using the non-static model?

You can do this easily in Nifskope.

Expand the bhkCollisionObject branch, highlight the bhkRigidBody line.

In the Block Details change the following values.

Layer - from OL_Clutter to OL_Static
Layer Copy - from OL_Clutter to OL_Static
Motion System - from MO_SYS_SPHERE_INERTIA to MO_SYS_BOX_STABILIZED
Solver Deactivation - from SOLVER_DEACTIVATION_LOW to SOLVER_DEACTIVATION_OFF
Quality Type - from MO_QUAL_MOVING to MO_QUAL_INVALID

Save the mesh under a new name and create a new static item in the CK.

My mod Home Construction and Decoration allows for any grabbable physics based object to be turned static until it's picked up again.
http://skyrim.nexusmods.com/mods/22791/

It's much nicer than making a new mesh for every object you wish to do this to.


EDIT: Didn't see that you didn't want it to be removeable. Sorry.