It does not change.

It always stays the exact same disguised name for any and every auction, regardless as to how many auctions u enter at once, over the same day or a week/month.

Everytime I partake in a ebay auction, my disguised ebay calculated name always appears the same to me , or to any other viewer.
The only time any part of it changes, is if additional feedback has been given and the number at the end increases numerically. 

Hope it helps. 

100% right is never changes.
If you want to find out the bidders name just wait until feedback is left (if the win the item) and you will then know their "code"