Compactlogix Set Points Syncrho. using modbus

Hi, I´m using the modbus slave program from Rockwell and I want to syncrhonize some set points. My problem is that when I send values to the CLX holding registers I move these values to the tag, but when I try update the tag from HMI, the move instruction overwrite it with the old value sent by the modbus telegram.
I have heard about a programming technique to do this but haven´t found it yet. I hope you can help me!
Br
Jorge