Convert Act Curtain to Tableau

Just to be clear you want to re-rig your existing bi-parting Main to open as a tableau, correct?

Can it be done? yeah.

It probably won't give you the results you want and it might possible damage you curtain. Most tableau's are either made from lighter fabrics or they are rigged, from the beginning, to be able to resist the stresses that are kind of unique to the tableau rigging. Increased number grommets, especially towards the center of the curtain are a must. For the best results you would need to remove the track, add grommets to the first 6-8 feet of the center side of the curtain panels, add ties to the grommets, tie off to the batten, then rig the trip lines to the back of the curtain. the best way to add the trip lines is to plot out the path of the lines then select the number of points wear you want the swag folds to happen, then sew on stainless rings at each point. Then add rings to the bottom center corners and tie-off the trip lines. Rig pulleys to the outside ends of the batten and run the lines back to a common point left or right and/or rig them to spot blocks and run the whole thing from the rail.

If your main is old you run the risk of it tearing at the points where you add the rings < I suggest whipping them to seams between breadths so the stitches don't show through on the front of the curtain.> You also run the risk of pulling grommets through the webbing because of the forces imposed on the center points of the curtain. Cotton velour is going to drape differently than IFR/polyesther and depending on the weight of the fabric you may or may not like the results.

None of this is hard it's just a lot of work.