I'm using Chisel-MC1.10.2-0.2.1.47 and TConstruct-1.10.2-2.6.5.

For the life of me I can't get Seared Stone to chisel into Seared Bricks.
I tried adding "B:seared=true" to the list under "features {" in config, but that didn't work.
All the variants of Seared Stone are listed as "tconstruct:seared".

Not sure why it's not working.

Any help is appreciated.

You can't add features there, that's not how it works. To customize chisel use a mod like ModTweaker.