don't think you need DNA Center for that, you can create an AP filter with a AP regex name and apply new RF Tag to this filter and it will be applied to all AP matching regex expression.
go to configuration>tags&profiles>tags>AP>filter, click add
Rule name : any name you want
AP Regex name : TEST_AP* (mean apply it to any AP whose name starts with TEST_AP and anything after that (*), change it to your 100 APs, whatever is common in their name, you can play around with regex to match your naming convention)
assign tags including RF tag.
if it does not apply, reboot APs, you can reboot all in APs within a site tag through CLI
I used this last week on my C9800L with the APs in local mode (17.3.4c). This worked, the APs were already registered and it applied the config.
When I tried this filter on my Cloud 9800 running the same code, it didn't work. The APs are in Flex Connect mode. I put in the exact name of the AP and it didn't apply the new tags. I then rebooted the AP and it did not apply the new Tags.
Does anybody know if the filters work in Flex Connect mode?