I live in Montreal. My destination is Madinah, Saudi Arabia. My current flights are from Toronto to London, UK, to Jeddah, Saudi Arabia and then finally to Madinah, Saudi Arabia. I'm trying now to add a flight from Montreal to Toronto and also when I return back home. I would like to know if that is possible without making any changes to my existing flight times of departing and arriving. I basically just want to add Montreal to Toronto when I depart and Toronto to Montreal when I return. Also if adding this flight is possible, I would then like to know what the process would be for my baggage. Would I have to recheck them to their final destination once I arrive in Toronto, or can I just do that when I leave from Montreal straight away? I also have the same question about the baggage when I return.
The answers is... depends. You'll need to talk to your travel agent or airline.
Basically, it's going to depend on the exact fare construction you've booked. If it's something like (anywhere in Canada)-UK-(anywhere in Saudi), it should be possible to add in the flight, and if you're lucky it might even be free -- although change fees will most probably apply.
However, if the airline in question only flies to Toronto, you'll have to fly somebody else for the Toronto-Montreal leg. This will obviously cost money, plus you'll probably have that change fee again, so it might be cheaper to just buy entirely separate tickets.
If you change your tickets to include the flight, your connections are guaranteed. On the way to Saudi, you can check your bags through from Montreal all the way to Jeddah, where they'll go through Saudi customs before you continue to Medina. On the way back, you'll have to take your bags out at Toronto for Canadian customs, then drop them off again.
If you buy a separate ticket, your connections are not guaranteed, meaning that if your flight into Toronto is late, you risk losing the entire Saudi trip. You will also have to recheck your bags at Toronto both ways.