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.