Yes, just I delete all the faces at the top/bottom of the cylinder. Then I grab the edge and extrude inward. If you still want to close the cylinder then extrude again, and just click 'merge to centre' under 'edit mesh'.

The insert edge loop won't work on the original faces because they are triangles. If you want to edit the original faces, you have to delete them, extrude the edges inward as close to the centre as possible to recreate the same shape, but don't merge to centre. Now each face will have 4 vertexes and you can use 'insert edge loop'.