Use a block to cut the skirting.
When building a staircase, I sometimes need to cut back the skirting to allow a newel post to attach directly to the framing. With finish nails, I tack a straightedge guide block to the layout line. The guide block keeps my Japanese pull saw tracking straight. The pull saw has a thin, sharp blade that makes a neat cut. Afterward, I carefully pry off the guide block and fill the nail holes.