Permanently update parameter value using "Command line" custom script

Hi all

I'm trying to figure out how to update a parameter value using a "Command line" custom script Build step.

All examples and documentation I have found says that:

echo "##teamcity[setParameter name='parmname' value='something']"

should work. And it does. But the value is not stored permanently in the parameter. So if I go and browse the value via the GUI, the parameter holds the original value. 

Anyone know if I am doing something wrong ? Or can explain what I am misunderstanding ?

Thanks in advance