You can just use CLI to disable.
jtac-SSG5-r002-> unset alg sip enable
jtac-SSG5-r002-> get alg
MSRPC ALG : enabled
SUNRPC ALG : enabled
SQL ALG : enabled
SIP ALG : disabled
RTSP ALG : enabled
H323 ALG : enabled
MGCP ALG : enabled
SCCP ALG : enabled