I just re-tiled a bathroom floor... and noted too late, that we now have the toilet flange sitting too high for re-installing the toilet. The sewer pipe and flange are cast iron, I think. Can we cut it off with a grinder and re-install a new flange? Does the flange just slip onto the pipe, or does it have to be leaded? How high should the top of the flange be from the surface of the tile? Any help you can give would be appreciated. If done by a plumber, can you give me a ball-park figure for a job like this? Thanks

You do have options here.

Can we cut it off with a grinder and re-install a new flange?
That's one option. You can break out the old flange, remove the lead and oakum joint and install a twist-
Loc flange, (see image) **OR**
You could take a block of wood and a hammer and tap around the flange. The lead joint will loosen and you can tap the flange down to the floor, cut the extra cast iron off with a grinder and Recaulk the lead joint.

How high should the top of the flange be from the surface of the tile? The top of the flange should be flush with the floor.

Good luck, Tom