(1) The path is stored in the registry:
HKCU\\Software\\Patchou\\Messenger Plus! Live\\<email>\\Preferences\\LogDirectory
(2) You only have to upload the ones with certain users, and if you want to modify it just copy the file to another directory, change it, and then upload it. If they're XHTML you can delete individual messages easily, and they contain times so you can only keep the certain times.
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