No. You can't set the slider to be set as a default score.
It's best practice to _not_ set the slider to an initial number. You'll notice the sliders don't have an initial value set. The logic behind this is - when the slider score is submitted by the end consumer you know it's the score they want to submit as the consumer has moved the slider from the initial position. i.e they have press the plus / minus or slid the slider along the rail.
If the slider was set to 10 by default and the end consumer submitted the survey - you would have a question mark over questions submitted as 10 because you don't know 100% that the person wanted to give a 10 or did they completely miss the question and 10 get submitted by default.