There are actual several ways of doing this.
You could arrange your single and/or block registrations in regular folders like on your computer.
You could make a folder with dinner music and one with dance music or perhaps arrange them by genre.
Also a block can hold up till 20 single regs and not just 10.
When you add a new registration be it single or block, the number assigned is auto incremented for each new addition. If you want to change this number you will have to hook up the Audya with your computer. If you change the numbers make sure that no two registrations share the same number.

[This message has been edited by Morten Jonassen (edited 09-13-2009).]