When a new widget or banner is created, a new affiliate id is assigned to it and it cannot be replaced by another aid.
You can track all activity and statistics per aid by visiting Performance > Product Performance.
You can also group them together, to get an overview of the combined results of all the widgets you have added to your website(s).
More information on the Groups feature: https://affiliates-support.booking.com/hc/en-us/articles/360000631306-Groups-Performance
Good to know: whenever you create or edit a widget or banner, you can have its result pages show your logo, if you have a co-brand already.
How? By choosing your url from the dropdown 'Where does this product link to? (Select one of your Booking.com partner platforms below)'.