Alignment is a paragraph-level attribute. I suppose you could create a paragraph style in which everything is blank but the alignment...?

Also, a brief training session can make a world of difference. I started a new job 6 months ago, and one of the first things I did was to create a template for some QA testing reports. I did a 1-hour session that first went over how styles worked, then how the new templates worked.

In that session, I stressed the need to use ONLY the styles in the template, and not use the formatting tools on the toolbar (I labeled that section of the menu "The Bad Place").

In your case, it might be useful to spend some time to introduce them to the table styles and how they work, and how to use the Bad Place controls to tweak as needed.

The final thing to stress is that if they really screw up the table formatting (and they will), they can just use the Clear All command in the Styles pane to reset the table back to the original table style.