Daniel, thank you in advance, by his answer quick.
But pay attention to the second assignment, the new value is append to the end of the previous content of $fU variable and isn't overwriting the $fU variable with the new value. This behaviour is what one I expected.
That behaviour is Design definition?
Beforehand, let me I join the Kamailio development community.
Best Regards CMA
https://www.kamailio.org/wiki/tutorials/faq/main#why_changes_made_to_headers...
time?