Sip extension Additional fields

I am wanting to add additional sip settings to freepbx ,
just trying to workout if it is possible build a module to add the extra settings to the sip table,
or am i better building a new table with these settings and creating a “sip_additional_post.conf”

end content will look like
101
cisco_usecallmanager=yes
subscribe=102
subscribe=103

Any hints would be greatly appreciated

Regards

D