I have a very complicated and perforated structure that i'd like to run in symmetry to reduce DOF. When cut on the right plane (symmetrically) the perforations cut the part into many faces which have to be selected.

When applying the faces in the symmetry fixture dialog box every face seems to take an age to select (seems to try and rebuild the mirrored part in preview). I put all faces in a selection set and then used the selection set in the Fixture dialog box the computer ground to a halt.

Is there a way to defer the preview / mirroring of the part until all faces are selected.