Mounting a motor and light on the 27 will not ruin it, and you can keep the treadle part. The treadle part has it's advantages, you can get a fantastic feeling for the rythm of stitching and movment of the material on a treadle. Have you had the chance to use your 27 as it is? All my machines are electrical, my 201 probably was converted from treadle to electrical early on in it's life. I wish they left the treadle parts on the cabinet, even though they are a very heavy.
On the other hand it might be just as easy to get a full size machine like the 27, 127 (or other full size model) already with an electrical setup. The smaller solid hand wheel might be an advantage with an electrical setup compared to the spoked hand wheel. I have a spoked hand wheel on my electrical 201 and I am thinking of getting another one which was originally set up with motor and light from the start. Some of the small cabinets for electrical machines are very nice too.