I found a helpful answer from Matt on this thread:
Simply go: Settings > User Properties > Design > Check the 'Always Show Design Menu Items' box.
Now simply right-click on the dimension back-ground and you'll see a new option in the menu 'Custom Format Cell' - click this and away you go!.
This allows you to create custom styles for tables. However, I was unable to save the custom style onto a theme file (.qvt) which is my primary need on the custom table style.
Hope this helps.
I am not sure what exactly you need to customize in table, but you can always set different settings for text, background, and fonts in Visual Cues property. Also you can apply same settings to other tables in the app, by using linked objects. Linked objects are availabe starting Qlikview 10 version.