i have a model with some modifiers on (subdivision surfaces and solidify) and i'm not able to apply those modifiers with the shapekeys on, but i want to keep them, is there any solution beside doing the entire thing again?
Lets say we have a mesh with 2 shapekeys: 1 basis and 2nd Big Ears.
Create a copy of the mesh, select the copy and delete the basis shape key, then the big ears shape key.
Select the original and delete the big ears shape key, then the basis; you'll end up with two different meshes, one original and one deformed.
Apply your modifiers in both the objects (starting from the upper in the stack).
Then create a basis shape key for the original mesh, select the deformed, shift select the original and use the "Join as shapes" function.
To anyone reading this in 2021, there is a discussion with a script automating this for blender versions 2.8 onward: Apply Modifier for Object with Shape Keys Add-on
This should make it easy to solve this problem especially with several blendshep on a single mesh.