Wow. It does appear to have disappeared. Quite unfortunate considering the time I put into writing a reply. Oh well.
First you need a tool that edits Fable files. I highly recommend
Shadownet. It's exactly like FableExplorer because it is FableExplorer, it just works better.
And I have a better way for getting stupid huge amounts of experience. It's easier and cleaner.
In ShadowNet, scroll down to OBJECT. Click the plus sign next to it, scroll down to 4292 - OBJECT_HEALTH_POTION and double click that.
In the left pane of the window that opens, click the plus sign and then click CDefs. You'll see a lot of links to other entries that change the way the potion is used.
Find the one called CBonusItemDef (third one) and click the first blue link in it. The second link just opens up another of the same window.
The CBonusItemDef is completely mapped - that means everything it does is clearly labeled. You can make it give you as much health, mana, fat, experience, morality, agreeableness, attractiveness, and scariness it adds to your character. It can even be made to give you negative morality (for evil), agreeableness, attractiveness, and scariness. Other things you can do are make it an alcoholic drink with an extremely potent alcohol effect. Or make you temporarily attack faster. Or increase your max health and max mana to their maximum.
When you're done making changes to the health potion, click apply changes, Actions|Save Mods and Run Fable.
In game, drink a potion, become superman, crush the skulls of your enemies, have fun.
Should you run into any problems whatsoever, consult
this post.