If you want to rename all the children Items within a product line, then you can!
Let's say that you created some inventory but perhaps didn't care too much about the names / IDs of the actual children items.
The actual bikes (in yellow) are named generically and automatically; Bike_302, Bike_302...
But then, you want to give them a named sequence that means something in relation to your actual bikes.
You can do this by visiting the actual Product Line and scrolling down to where you see this section:
add or edit the Short code / Name stem field to be what you want to call your sequence of items.
Here I've named it BK for my series of Bianchi Kuma bikes:
When I choose the rename option it will rename all the items in this Product Line according to that sequence:
BK1, BK2, BK3 etc