I did learn from tutorial, but I think that tutorial was only ever shared with the staff of Inane and whoever that author personally linked to it, so I don't feel privy to spread that tutorial around (I'd have to do some serious digging to locate it too, and I'm not even totally sure I have it at all).
I can't point you towards one but since those days, editing Shounen Jump magazine scans has exploded, so there's probably a tutorial for it somewhere?
Erm back then I did also come up with my own way of doing it but I really doubt its the best way of doing it. Off the top of my head, it went something like this...
- Level page
- Flatten image so there is only one layer
- In Channels palette, click on "Load channel as selection" which is the circle at the bottom of the palette (this will select all the black areas) and hit delete
- Create a new empty layer under that one
- On that new layer, using the Pattern Stamp Tool, select an appropriate tone from your library of tones you made beforehand and brush in where it should go
- If there are residual old tones, erase with the Eraser Tool
- Duplicate the image layer as necessary to give the lines/darks the weight they should have
- These steps do nothing for black areas with no tones, you still gotta fill those in yourself
Given the speed that some tone-replacers like those at Binktopia release at, I'm sure there are more efficient and effective ways of replacing tones now. Back when I was doing it, I think we were one of the first at Inane.