Asidert

It is possible to restore it back to 10 votes if you started with 10 votes, and you clicked the upvote button by mistake (taking it to 11 votes), then you will be able to restore it back to 10 votes just by clicking the upvote button again if you clicked it accidentally.

By clicking the upvote button by mistake (taking it to 11 votes), then clicking the downvote button (taking it to 9 votes), you will change your upvote into a downvote, which will result in a total vote of 9 votes. In the event that you click the downvote button again, you will be able to undo your downvote, which will result in your vote total returning to 10.
 
There may be a case where it would be clearer to the user if (for example) there was a way to highlight the currently-applied vote button, but it is certainly possible to restore the previously-applied vote total if one accidentally clicks a vote button.