Hi mustardman,
FreePBX version is not related to the asterisk version. Fop2 officially supports asterisk 1.4 , 1.6 and 1.8. And it works well with all those versions. It also works with asterisk 1.2, but some feature do not work (you can perfectly use it anyways with asterisk 1.2, but you will miss some queue functionality).
The extensions_override configuration file is not a key component in fop2, it is just to do a tight integration with freepbx dnd featurecodes, and it is dead easy to make it work for any freepbx version. You have to copy the feature code macros and add 3 lines as in the included extensions_override_freepbx (that is for freepbx 2.8).
The extensions_override_freepbx is not mandatory, You can very well have a fully working fop2 with no two way integration between freepbx dnd and fop2 presence. Just skip that confgiuration. That is a *bonus* feature if you want. fop2 will work the same if you have that two way relationship working or not.
If you use FreePBX 2.9 and you want to relate fop2 presence to freepbx dnd, then do what Andy suggest, replace DEVSTATE with DEVICE_STATE in the supplied extensions_override_freepbx.conf file. If you fail to do that, fop2 will work anyways with freepbx 2.9.
So, the status is that fop2 is fully working. Configurations can be modified. Dialplan contexts can be modified. They are there to be modified if needed.
Best regards,