[sr-dev] [kamailio/kamailio] Why can't set_body_multipart and append_body_part* functions be used from ONREPLY_ROUTE? (Issue #4149)

rodrigodc created an issue (kamailio/kamailio#4149)

Hello,

Is there a strong reason why the following functions from [textops](https://www.kamailio.org/docs/modules/5.4.x/modules/textops.html) can't be used from `ONREPLY_ROUTE`?

- [set_body_multipart](https://www.kamailio.org/docs/modules/5.4.x/modules/textops.html#textops.f.s...) - [append_body_part_hex](https://www.kamailio.org/docs/modules/5.4.x/modules/textops.html#textops.f.a...)

I need to add ISUP to outgoing `SIP/18x` replies which already have an SDP body and would like to use those functions for that.

However, they cannot be used from `ONREPLY_ROUTE`, just as they can from `REQUEST_ROUTE` (which I use to add ISUP to `SIP/INVITE`).

So I am considering sending a pull request allowing them to be used from `ONREPLY_ROUTE`, but first I would like to know if it makes sense.

Thank you.