Removal of the old yellow and brown needles should open it up and allow more light and air in to (hopefully) promote back budding. What you really want is lots of healthy growth, particularly long runners to induce back budding. Lots of energy means lots of growth.
Unfortunately, some of the old bonsai literature (incorrectly) advocates pinching to promote back budding. Pinching does not promote back budding, but instead slows growth and increases density on the tips. Pinching is for finished trees.