I do not have actual instructions, but have seen some youtube videos of the two methods, ie. removing the top completely, or drilling holes in the top and inserting the ink through the holes. Regarding the clip, most people in the videos I've seen just stick a piece of insulation tape over the exit port, instead of using a clip.Do you have instructions on how to refill your cartridges? Please link so we can see.
Thank you for the comment. There seem to be a lot of uncertainty around this, i.e. your test that canon's GI-490 ink doesn't work, whereas @The Hat, comment that any canon formulated ink should work in these cartridges. I have found the same locally as well, where some vendors indicate that you can use GI-490 ink whereas other is of the opinion that you can not.So I agree with stratman's recommendation of trying the locally available inks.