Does this support advanced format(4K) disk backups as well?

As 512 was the actual sector size earlier and now 4K drives are common, is it supported? if not, what are the changes that needs to be made?

First thing that comes to mind: why wouldn’t it?
Urbackup just looks at the filesystem, not the (logical) block device or it physical device, where your 4k sectors are. I guess a better question would be what filesystems does urbackupclient support.
So far my rant, here is your answer: yes, no changes.
Why: look around; this software is used a lot on current hardware, from what i read most vendors use AF since 2010. If this was an issue i am sure somebody would have mentioned it here by now.

On multiple places, sector_size is coded with default value of 512 and the same used for all the calculations.