best for YC staff to respond, but i would think yes - since YC gives a greater weightage to the quality of the founding team, than specific ideas. but then looking at it from another angle, wouldn't it send a message that you have a problem in staying disciplined and focused which is critically important to build a solid company?

in conclusion, my recommendation is to choose one among the two ideas - and then use the second as reference work to demonstrate your entrepreneurial prowess.