I used shape keys to create a middle shape between other two. Can I now remove shape keys and 'apply' them as a modifier to the resulting mesh?
Try creating a new shapekey by pressing the arrow under the add/remove buttons and selecting new shape from mix:
This will create a new shapekey from the current mix. You can then delete all the shapekeys, making sure you delete the new one last.
This gives you a shapekey-free mesh with the shape from the original shapekey mix.
You can use the Corrective Shape Key addon. It's under Community > Animation in Addons.
Once installed, just find the desired blend you want, press the black triangle in the Shape Keys panel and choose Create duplicate for editing. This will apply the state and create a new copy while preserving the old one with the keys.
There is a way most people don't know.
Go to File > User Preferences > select Community supported level Object -> Category Oscurart Tools. For Blender version 2.8+ select Addons > Only Community and type in the search bar
os now you should see Object : Oscurart Tools.
Tick it to active and save settings.
Select the mesh you want to copy (no edit mode needed)
Press enter to open the search function and then type
Make sure its typed with small letters and spelled the right way.
If this happens then you didn't select the mesh.
If you get this option you did it the right way:
- Select Object to Mesh
Done, now you have a copy of the mesh the way you setup the shapekeys and or pose but without shapekeys.
Note that it also applies modifiers like subsurface etc. and because its a copy you still got the original mesh with all modifiers, bones, shapekeys you started out with.