Looks good to me. From the documentation this feature should work like this in the first place.
But I did a review of the code, and it seems this feature was modified to actually work in the (in your opinion not desired way), but probably the docs not adapted. See below.
So probably a better idea is to introduce another mode "2" for the rtpengine_allow_op parameter which then trigger the desired behaviour.
commit 5a537506141027ca3d3ef87f49913ab628c30690 Author: Stefan Mititelu stefan.mititelu@1and1.ro Date: Mon Dec 7 13:30:02 2015 +0200
rtpengine: Allow op for all deactivated machines If allow_op modparam enabled, send commands to the disabled machines for the existing call. So far this was done only for manually deactivated machines. This is useful because there might be cases of proxy timeout, cases when you may want to still allow the operations for the existing calls.