With regards to customization, there are a few ways to go about it but not directly via the DBR directive at the moment.
For the drill contents itself, there are APIs that could help you out to getting those:
Which you can combine with the DBR’s custom context menu so you can create your own modal (call cellGetDrillNames, then pass the drill name you wanted into cellGetDrillNameTransactions to get the results in JSON).
Another alternative is to make the source of this table as a link, if it is part of a simple table report for example, to open another page instead where you can pull out the drill transactions for that particular number / cell.
That could be a nice feature to have in there! Would also be great if you can send this through to your local Cubewise contact/office as a feature request. Thanks!