Use an HMR to convert a 5xx or 408 reply to a 403
Here's a handy HMR for converting reply codes. Use case would be where a downstream device does not re-route based on the 5xx | 408, but does on a 403.
You can find out more about the use of @status-line from the 6.3.0 ACLI Configuration Guide, publicy available here. Specifically, page 403.
sip-manipulation name 5xx408to403 description Change all 5xx or 408 responses to 403 split-headers join-headers header-rule name CheckFor5xx header-name @status-line action store comparison-type pattern-rule msg-type reply methods INVITE match-value new-value element-rule name is5xx parameter-name type status-code action store match-val-type any comparison-type pattern-rule match-value ^5.+ new-value header-rule name CheckFor408 header-name @status-line action store comparison-type pattern-rule msg-type