I goggled
phpsqldiff. Seems pretty nice at first glance.
Otherwise you could give the old fashioned programmers way a try:
To attempt to patch your modified DB to the latest and greatest PEQ release I would try the following:
Make yourself familiar with the GNU patch and diff commands. These are available under Unix/Linux and Cygwin.
Install the PEQ release your modifications are based on into a different database anf dump it. It's crucial that every line of the dump has the INSERT command. Even so you might stumble over CREATE TABLE parts(that's why I recommend setting at least -u20 for the diff command)
Install the newest PEQ release into another database anf dump it too.
Diff the two dumps to make a patch file.
Check the patch file for any rule changes that might have impact on your server.
Dump your customized DB and try to apply the generated patch file on it.
Of course you could also make an diff of your modified database to the one it is based on and try to apply it to a recent release. But you'd have to worry about your user tables.
Once again, this is just I would try and will certainly need quite some editing on the resulting patch. Maybe it would be simpler do a diff per table and not the whole database.
Btw.: I had a chat with our resident database guru and he said to turn on logging for the relevant tables. To do that under MySQL you have to use a trick since you only can enable logging on whole databases(-> major performance impact). I might not have understood it correctly cause he has an heavy russian accent, but I think me meant symlinking/linking the relevant tables into another database.