Can backup update instead of creating a whole new copy of everything?

Two points to this post: 1) Can the built-in backup tool update, instead of re-create, a backup? 2) If not, can I get the option to point the backup button to an app of my choosing?

I currently use BART (B.ackup A.nd R.estore T.ool), a nice portable backup app, to backup my PortableApps flash drive. It allows me to backup the entire drive, ignoring specific files (*.tmp, etc.) and folders (app caches, etc.). I like it because I can make a complete copy of everything and then simply update the contents every time afterwards. That way I don't have to make a whole new copy of my 16GB flash drive; it will just replace changed files, delete removed files, and add new files.

I used BART before PA.com suite had a built-in backup, but now there's a backup button and I'm deciding if I should switch. So, will the built-in backup tool do updates too, or do I only have the option of copying the entire contents or the 16GB drive every time I run a backup? ...assuming I want a backup of the drive, not just my settings/personal files.

If not, how tough would it be to add an option to point the backup button to an app of my choosing (BART in my case)?