Are you using no-warnings True or ignore-warnings true?
Sounds like you may need to use set-if-exists true (see example in my last reply and below).
This is a working example:
mgmt_cli add service-tcp --batch tcp-services.csv
tcp-services.csv
name,port,ignore-warnings
http-new-1,80,true
http-new-2,80,true
http-new-3,80,true
That adds new tcp service using port 80
This is an updated tcp-services.csv and it effectively includes set-if-exists true
name,port,color,ignore-warnings,set-if-exists
http-new-1,80,Olive,true,true
http-new-2,80,Red,true,true
http-new-3,80,Green,true,true
There is also the clone option, in case that helps.
clone service-tcp name "http" new-name "tcp-new-81" port 81