I'm not aware of any ClearOS app that will do this. However, since it is CentOS based there are many applications that could easily be installed on CentOS that can handle this.

Look at Kamailio, formerly known as OpenSER and SER (SIP Express Router). http://www.kamailio.org/w/

In addition, there are other things that can be utilized including Asterisk and SIPXecs that are more softswitches but still can perform these functions. There is an article on the ClearFoundation.com site that explains how to install SIPXecs under ClearOS.

Any of these will provide far more capabilities than what can be done on a SonicWall.

In fact, having had to support a SonicWall for a while for a non profit entity, I came to absolutely hate the device. While it has tons of capabilities, doing things that are VERY simple on other devices like configuring Port Forwarding that takes about 20 seconds on ClearOS, involves multiple rule configurations that take forever to enter, even longer to test to ensure it was done right, and that is a major pain...

BTW - assuming you're still here, what type of SIP header manipulation are you looking for? Just basic stuff, or something more involved?