Last time I dealt with this, there were only 2 options:

  - Save the expression again to the library - unchecking ALL non expression morphs

  - Use an intelligent text editor and strip the non-expression morphs

Loading the figure with only expression morphs injected will still zero out the other morph channels.

I have tried several cleaning tools, but none of them would do expressions

The text editor option is the easiest - if you have a text editor which does macros.

It is a pain, that is why I now always check if expressions leave morphs alone. If the description does not mention it, assume it does not leave them alone