use a wise
 

After doing my share of curseing and geting my fingers cut enough times trying to remove old sticking offroad tiers I made a set of grips that fits over the jav on a ordinary workbench wise. Its just a bracket that clamps around the head of the wise with a curved plate 30 cm long with(in my case) the same radius as a 17 inch rim.Let the air out. Open the wise, place your wheel between the two plates,about 3-4 mm from the rim and tighten the wise,once the rubber comes lose on that part simply open the wise rotate and tighten again. Works like a charm:thumbup1:

Flats on the road are ofcourse still a pain in the ass:rolleyes2:

Tom.

Whilst riding your trail bike off-road, with low tyre pressures, this extra lip will help to keep the tyre bead against the rim. If the tyre breaks away from the rim, then the wheel will spin inside the tyre and rip-out the tube's valve! Then you'll have yet another flat tyre to worry about.
Chromed steel rims on bikes such as the Honda CG125 for example wont have this lip, as they will be ridden on the road with higher tyre pressures to keep the tyre in contact with the rim.

So Size does count
 

As GSWorkshop says tire leavers are definitely required, as another said a liquid soap or a water based grease (don't use conventional grease) makes the job achievable.

As far as tubeless goes. How can you have a tubeless fitment on a spoked rim. Is there some magical tire or sealing agent I've not seen. Please forgive me for my ignorance. I've never seen this.

As far as I'm aware tubes are a requirement.

As for machining your rims. I would be extremal cautious modifying the rims. They are designed to prevent you tires breaking the bead during sideways impact of force from sliding. Changing this may result in your tire collapsing on it's self. In the case of a tubeless tire it would deflate, in the case of a tube it would likely pinch resulting in the same very nasty result. A very quick get-off.