Sure it's possible. But, why would you want to screw up a good sensor by doing that? If you feel like it's too much trouble for you to do the job the right way, you need to pay someone else to do it for you.
most of the time by the time the sender goes bad the wires are there too. If you tape the new wires to the old and are very careful you might pull them through.
I guess it depends on where you want to splice into the trim wires.. Obviously its better to replace the sensor along with its new leads, but if you splice up where the wires go through the transom and you solder the joints and put Marine Heat shrink (has glue inside) over the joints, it should be okay..
I have used Starbrite Liquid Electical tape to repair fraid wires on my senders. While its not the perfered method to solve the problem it has worked so far. You could probably do the same if you decide to splice the wires. Use several coats. I know what you mean about how complicated it looks to replace the senders. Its no small job but doing it right the first time is the best way to aviod future problems with a patch job.
Good luck
