How to renegociate codec from the dialplan

I need to renegociate codec in dialplan after answering the call.
The asterisk receive an incoming call with video (h264), then connect the call to a queue (video codec is negociated between asterisk and caller). After a while, the call exists from queue to a timeout and redirect in the dial plan to the voicemail service (using VoicemailI dialplan function). I don’t want video on voicemail, but I found no way from dialplan to sent a reinvite to caller and renegociate codec …

Such a command exists on dialplan or should I modify the channel.c to create it ?

Thanks for your advises.