delete certain text occurred within curly brackets

I have sample file as follow :

 WEA {
     Direction = Input
     Tag = WriteEnable
     PortId = "A"
 }
 MEA {
     Direction = Input
     Tag = MemoryEnable
     PortId = "A"
 }
 CLKA {
     Direction = Input
     Tag = Clock
     PortId = "A"
 }
 TEST1A {
     Direction = Input
     Tag = None
     TieLevel = TestBench
     PortId = "A"
     SafeValue = "1'b0"
 }

I am trying to replace PortId = "A" as PortId = "A B" but in only the CLKA{ } module. I tried to run certain modification on code given as

sed ':again;$!N;$!b again; s/{[^}]*}//g' file

on previous post remove text within curly brackets

I tried this sed ':again;$\!N;$\!b again; s/CLKA {[^}]*}//g' but deleted whole CLKA { } module