I thought the problem might be aircraft-related as removing the modded Stuka files solved the crash problem completely. This is odd, as I haven't made any significant changes to aircraft in the last week or so, so it could possibly be caused by AA guns, maybe the Bren AA which there are plenty of in Mersa Matruh and which the bots rarely if ever seem to use.
But I managed to play for about 30min on Mersa Matruh today, using the modded aircraft files, without any crash (I exited the game after 30min rather than it crashing) so I think the minimod is stable enough for a "beta" release (see the new thread with download link)
Also, I think I've got somewhere in solving the bot disembarking/bailing/switching position issue - if you open aibehaviours.ai and find this line under the FixedWeights table (which is used by both stationary guns and all non-driver positions on vehicles):
aiSettings.setBehaviourModifier Change 0.0
Change "0.0" to any positive value, and bots will be able to exit or switch vehicle crew + passenger positions. I set it to 1.0 - this may not be the optimum value (too low, and it won't have much effect - too high, and bots will keep jumping in and out of vehicles) but I did notice, for example, bots leaving AT guns when there were no enemy vehicles around, and tank hull gunners switching to the driver position when you (the driver) exit the vehicle.
A fair bit more work will probably be needed for bots to use APCs and trucks effectively, so I haven't included this fix in the 1.1 release of my mini-mod.