how to analys if the part break or not at a certain deformation

Load your tube with internal pressure (or force) to expend tube ID at .3 mm to fit assembly requirement. (This is the way to simulate the tube in assembly mode). Run the Simulation Study and analyze results. Check if:

1. Maximum von Mises stress in deformed part is not greater then maximum Tensile Strength or Shear Strength for PEEK (material of your part).
2. Maximum deformation in part must is not greater then maximum Tensile Elongation for PEEK.

If for both questions the answer is “YES”, you are OK and part will be not destroyed during assembly.

You could use the Reference Geometry option under Fixture or Prescribed Displacement under Loads. Choose the faces that displaces and the direction, as well as the magnitude of to.3mm

Run the study and analyse the Stress results, make sure its below the Yield Strength of the material

A better way (IMHO) would be to apply a deflection constraint on the geometry that you expect to move the 0.3mm.  The pressure noted above would give a false stress in the part.