Thanks for the answer, very helpful

On 16.05.2020 11:02, Daniel-Constantin Mierla wrote :

Have you tried by setting the CSeq header inside $uac_req(hdrs)?

I tried, it simply adds another CSeq header, not replacing the generated one (I also tried with User-Agent header)
I may have to replace it manually on tm:local-request event route

Then there is the option with t_uac_send() from tm module:

  *
https://www.kamailio.org/docs/modules/stable/modules/tm.html#tm.f.t_uac_send

 
I did not know about this uac from TM module
I tried the function, but it doesn't seem to accept variables as parameters... I must be doing something wrong, it is almost useless if it can't be used with variables

Thanks