Extended script Essential graphics

Hello!
I have a composition with Essential Properties where I control the Source Text from another composition. How can I script an Expression into the Source Text parameter so that it doesn't change the parameter inside? Right now, when I access the parameter through a script and enter an Expression, the value also changes in the Source Text of the original text itself. And it shows the following message.

This Essential Property is controlled by an expression in the Primary Comp, click here to override.

Is there a way to code a value so as to separate them?